In a large bowl, cream together 1 cup butter and 1 cup sugar for 2 minutes.
Add in 1 Tbsp vanilla, 1 egg, and 2 Tbsp of frosting and mix thoroughly.
Mix in baking powder, flour, and salt until well combined.
Line a 9” x 13” baking pan with parchment paper.
Add dough into pan and press dough into a flat layer.
Bake 15-20 minutes, until puffy and no longer glossy. The edges should just begin to turn a light brown.
Let cool completely, then spread the remaining vanilla frosting across the top. Allow to set uncovered for at least 1-3 hours, or for faster results, allow to rest uncovered in the refridgerator.
Cut into bars and sprinkle with red, white, and blue m&ms and sprinkles.
Add poprocks just before serving so they don’t melt.