Preheat oven to 375 degrees. Grease a 9x13 inch pan and set it aside. In a large mixing bowl combine flour, baking powder and salt then set it aside.
In a stand mixer or with beaters, cream together butter and sugar until fluffy. About 3 minutes. Combine egg, egg white, sour cream, and vanilla. Mix together until fully incorporated. Add the dry ingredients until all is fully combined.
Gently press the dough into the bottom of your 9x13 inch pan. Bake for 17-20 minutes until the edges are lightly golden and toothpick entered in the center is clean. Let completely cool and frost.
To make the frosting, Whip together butter, powdered sugar, and half and half until fluffy. Add vanilla. Add food coloring if using. Spread on the top of the cooled bars.
Updated on May 9, 2021Originally Posted on May 18, 2014