1 cup butter, softened
2 cups granulated sugar
¼ cup sour cream
2 teaspoon vanilla extract
5 cups all-purpose flour
1 teaspoon baking powder
½ teaspoon salt
1 recipe classic vanilla butter cream
Preheat the oven to 350 degrees and butter the bottom and sides of a jelly roll pan (half sheet pan).
In the bowl of your stand mixer (paddle attachment on) whip the butter and sugar until light and fluffy, about 2 minutes. Add the eggs and beat to combine, around 30 seconds. Add the sour cream and vanilla and combine. Sprinkle the flour, baking powder, and salt over the top of the ingredient in the bowl and then mix on low until completely combined.
Spread the dough evenly in the buttered pan and then bake for 16-20 minutes until the dough is set but still light in color.
Allow the dough to cool completely before topping with frosting and sprinkles. Cut into bars and serve.
I made these the day before, left them in the pan (frosted) and then just cut and served then when it was time. They travel well!
If you are having a picnic outside, it would be worth the time to chill these before putting them out so that the butter has time to firm up before going outside. Butter melts at 98 degrees, so don't leave them in direct sun or you'll have melty icing on your hands.
To get the 40 servings, I cut the pan into 5 rows of 8 bars.