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. I chose four pastel colors for my spring cookies!
9. 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.
10. Spoon frosting into small 12-inch disposable frosting bags. Snip off the tips.
11. Carefully slide all four bags into a LARGER frosting bag. I used an 18-inch bag with star tip attached.
12. Pipe frosting onto cooled cookie bars!