Preheat oven to 350 degrees F. Line a 9-inch square baking dish with parchment paper and set it aside.
Start by making the cinnamon filling. Using a fork, mix together the melted butter with brown sugar and cinnamon until combined. Set it aside.
For the blondie batter, in a mixing bowl, combine melted butter and brown sugar with a whisk. Add in eggs and vanilla extract and whisk until fully combined.
Using a wooden spoon or spatula, add in flour, cinnamon, baking powder, and salt. Mix by hand just until combined.
Pour about 2/3 of the batter into the bottom of the prepared baking pan. Spread evenly using an offset spatula. Sprinkle the cinnamon filling mixture over the top, using your hands to make sure it is evenly spread out. Top with the remaining blondie batter, spreading evenly. You may have some filling peeking out and that is okay.
Bake blondies in preheat oven for 38-42 until golden brown. Remove from oven and cool in pan before adding the frosting.
For the frosting, beat butter and cream cheese for 3 minutes until smooth, scraping down the sides of the bowl as needed. Add in powdered sugar and vanilla extract, and beat an additional 3 minutes until creamy.
Spread frosting over the cooled blondies. Cut into squares and serve.
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Notes
Mix by hand. No need for a mixer here, use a whisk and wooden spoon, being careful not to over blend the batter.
Let cool completely. These blondies are best when cooled completely. This allows the dough to rest and become chewy instead of gummy. If you want to serve them warm, heat in the microwave for 10 second intervals.
Want to make them thinner? Bake in a 13x9 for 25-28 minutes.
Store blondies in an airtight container in the refrigerator for up to one week.
Freeze cinnamon roll blondies in a freezer safe container (with or without the icing) for up to 3 months. Thaw in refrigerator overnight.