Soft and Chewy Frosted Rainbow M&M Cookie Bars Recipe

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Soft and chewy M&M Cookie bars topped with a sweet rainbow buttercream frosting. These frosted Rainbow M&M Cookie Bars are dreamy and delicious!

Soft and chewy M&M Cookie bars topped with a sweet rainbow buttercream frosting. These Rainbow M&M Cookie Bars are dreamy and delicious!

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I love frosting.

Preferably a good buttercream frosting.

And this one has rainbow colors. 

It also sits on top of a delicious, soft and chewy, M&M Cookie bar.

What’s not to love?

I happen to love a lot of frosting.

Give me a giant slice of cake, from the corner, with extra frosting please.

While some of my family scrapes the extra frosting off their cake, I pile it on to my slice.

How to Make Rainbow Frosting

Soft and chewy M&M Cookie bars topped with a sweet rainbow buttercream frosting. These Rainbow M&M Cookie Bars are dreamy and delicious!

Start by making your basic white buttercream frosting.

I make a larger batch so that I can put a decent sized “rainbow” on each individual cookie bar (or cupcake!). You can cut the batch in half if you think you prefer less frosting.

Start by beating softened butter for about 3 minutes using an electric mixer with whisk attachment. Scrape down the sides of the bowl as needed, until you see the butter turn pale in color, and smooth.

Add powdered sugar, milk, and pure vanilla extract.

Beat an additional 3-5 minutes until light and fluffy.

Now decide how many colors in your rainbow!

PRO TIP: Use Americolor gel colors for more vibrant colors that require less drops. Each of my colors was ONE drop of gel. 

Soft and chewy M&M Cookie bars topped with a sweet rainbow buttercream frosting. These Rainbow M&M Cookie Bars are dreamy and delicious!

I chose four pastel colors for my spring cookies!

Separate your frosting into small bowls (for each color). Add one drop of gel coloring to each bowl, stir until no white frosting is seen. Add more color if desired.

Spoon frosting into small 12-inch disposable frosting bags. Snip off the tips.

Carefully slide all four bags into a LARGER frosting bag. I used an 18-inch bag with star tip attached.

Pipe frosting onto cooled cookie bars!

This is also very pretty piped onto cupcakes!

Soft and chewy M&M Cookie bars topped with a sweet rainbow buttercream frosting. These Rainbow M&M Cookie Bars are dreamy and delicious!

Can I freeze frosting?

Yes!

Frosting will stay good in the refrigerator for 4-5 days.

However, should you choose to freeze frosting, it can keep in an airtight container for up to 3 months in the freezer.

Thaw frosting overnight in the refrigerator.

You may need to beat it again with your mixer to get it light and fluffy, and you may need to add 1-2 TBSP of milk too.

Soft and chewy M&M Cookie bars topped with a sweet rainbow buttercream frosting. These Rainbow M&M Cookie Bars are dreamy and delicious!

What can I do with leftover frosting?

Help! This was too much frosting for me.

While I personally don’t understand that phrase, I do know that some people don’t like as much frosting as I do.

In addition to freezing frosting, you can also pipe it onto sugar cookies for a delicious treat.

Or add frosting to these Bakery style brownies.

Still not sure how to use your leftover frosting?

Make a batch of Buttercream Truffles. That’s right, sweet candy made from your LEFTOVERS. Dream come true!

Soft and chewy M&M Cookie bars topped with a sweet rainbow buttercream frosting. These Rainbow M&M Cookie Bars are dreamy and delicious!

More Rainbow Desserts

My family loves these soft and chewy Rainbow Cookies. They’re basically M&M Chocolate Chip, with a delicious chewy texture!

These Rainbow Chip Brownies are made using the best homemade buttermilk brownie recipe! Move over Cosmic Brownies from Little Debbie…these are too delicious to compare!

You’ll love these decadent Rainbow Fudge Cookie Bars. Chocolate Chip Cookie bars topped with a sweet fudge and rainbow chips!

Soft and chewy M&M Cookie bars topped with a sweet rainbow buttercream frosting. These Rainbow M&M Cookie Bars are dreamy and delicious!

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Yield: 24 bars

Rainbow M&M'S Cookie Bars

Rainbow M&M'S Cookie Bars
Prep Time 15 minutes
Total Time 15 minutes

Rainbow Cookie Bars: delicious chocolate chip cookie bars topped with a rainbow buttercream (tutorial)

Ingredients

For the Frosting:

  • 1 cup unsalted Butter, softened
  • 5 1/2 cups powdered sugar
  • 1/4 cup milk
  • 2 tsp vanilla extract
  • gel food coloring

Instructions

  1. For the cookies, bake and cool one batch of chocolate chip cookie bars.
  2. Start by making your basic white buttercream frosting.
  3. I make a larger batch so that I can put a decent sized "rainbow" on each individual cookie bar (or cupcake!). You can cut the batch in half if you think you prefer less frosting.
  4. Start by beating softened butter for about 3 minutes using an electric mixer with whisk attachment. Scrape down the sides of the bowl as needed, until you see the butter turn pale in color, and smooth.
  5. Add powdered sugar, milk, and pure vanilla extract.
  6. Beat an additional 3-5 minutes until light and fluffy.
  7. Now decide how many colors in your rainbow!
  8. PRO TIP: Use Americolor gel colors for more vibrant colors that require less drops. Each of my colors was ONE drop of gel. 
  9. I chose four pastel colors for my spring cookies!
  10. Separate your frosting into small bowls (for each color). Add one drop of gel coloring to each bowl, stir until no white frosting is seen. Add more color if desired.
  11. Spoon frosting into small 12-inch disposable frosting bags. Snip off the tips.
  12. Carefully slide all four bags into a LARGER frosting bag. I used an 18-inch bag with star tip attached.
  13. Pipe frosting onto cooled cookie bars!

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Nutrition Information:

Yield:

24

Serving Size:

1

Amount Per Serving: Calories: 174 Total Fat: 8g Saturated Fat: 5g Trans Fat: 0g Unsaturated Fat: 3g Cholesterol: 21mg Sodium: 7mg Carbohydrates: 26g Fiber: 0g Sugar: 25g Protein: 0g
*Nutrition facts are an estimate and not guaranteed to be accurate. Please see a registered dietitian for special diet advice.

Recipe originally published April 10, 2012. Photos updated April 2019.

**There may be affiliate links in this post! By clicking on them, or purchasing recommended items I may receive a small compensation. However, I only recommend products I love! Thank you for supporting Shugary Sweets! See my disclosure policy for more info**

37 comments on “Soft and Chewy Frosted Rainbow M&M Cookie Bars Recipe”

  1. These are so pretty!! Awesome job. I love that icing 🙂

  2. I have a couple in our house that scrape the yummy frosting off. But you are right…more for us:-) Love the fun rainbow icing!!!!

  3. Frosting or no frosting…they both look good!

  4. These are gorgeous–love that rainbow frosting!

  5. I love the rainbow frosting! It’s so pretty and looks so intricate. I don’t have the patience to do that but I really want to now seeing yours!

  6. I love that frosting! I have never seen one with meringue powder and butter. It sounds SO good. I will be trying it for sure!

  7. I love all those features! Thanks so much for hosting.

  8. I love the rainbow icing–so gorge! And M&M cookie bars are my favorite.

  9. Wonderful recipe! I thik I’ll make this for Hubby tonight to take to twork. His co-workers are chocolate chip M&M fans!

  10. They look awesome, your frosting turned out so well! I just love the technique – such an impressive result and really not too difficult 🙂

  11. Those are so pretty! Love what you’ve done with the frosting … I am not the biggest, best froster, but I think I need to try that technique. Sometime.

  12. First off: M & M cookie bars = win!
    The rainbow decoration looks great! 🙂

  13. these are too cute! i’m adding them to my to-bake list. i love all those colors! awesome recipe. 🙂

  14. These look so cool. Who knew??!! And I’m right there with you on the frosting. That’s almost the best part!

  15. What a fun spring time treat. I will definitely have to make these. Love your blog and I am your newest follower. xo

  16. Great job on this frosting, Aimee! And the bars sound fabulous. The texture looks dreamy.

  17. People who scrape the frosting off are just odd. I LOVE frosting too!

  18. These are very beautiful!
    I really like the coloring

  19. Oh, yeah…. My kids and hubby would be thrilled with these!

  20. Very interesting idea for the frosting.

  21. I love cookie bars but have never frosted them. Looks like I better frost the next batch. Great recipe.

  22. Plain M&Ms are one of my biggest weaknesses. I love putting them in cookies and bars!

  23. That looks terrific. I know my family would love this. Come visit us. We have some fantastic things to share this week.

  24. Oh my goodness these look so yummy! I followed you over from Chef-in-Training and would like to invite you to share this, and any other posts, on my link party at http://www.michellestastycreations.blogspot.com. Have a great weekend.

    Hugs,
    Michelle

  25. As a child of the 70s I can never resist a rainbow, especially one as “sweet” as yours!

    Jenn

  26. These look so delicious! We’re so glad that you linked up to our “Strut Your Stuff Saturday.” We hope you’ll be back soon. -The Sisters

  27. These are so colorful and I love the recipe for the basic cookie bar!You are a party fave this week at the {what’s shakin’ link party} … I’d love for you to come on over, link up and grab a button!

  28. Tina

    I need help…i baked your recipe for blondies the other day…they were still raw…i rebaked them for another 20 min and still so soft u cant pick them up…i followed recipe exactly and i still cannot seem to find a good bkondie that is “chewy” without being sloppy raw like…

  29. Anna

    These cookie bars were a hit around here! My daughters made them and frosted according to your tips. Cutest treat ever!

  30. Suzy

    These are just what I was looking for! Adding these to the birthday party menu.

  31. These look perfectly decadent! I will have to make these for my daughter’s birthday party, she will love them!

  32. Kristyn

    We love m&m cookie bars & the addition of the cute frosting on top, would make them even better! My girls are all about rainbows!

  33. Taylor

    These bars are a DREAM! And that rainbow frosting is great! Perfect for parties!

  34. Yep, I just made some on Saturday because of that post. It’s amazing!

  35. Pingback: Perfect, Easy Double Chocolate Chip Cookies Recipe

  36. Pingback: The BEST, soft and chewy, M&M's Cookie Bars Recipe

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