Preheat oven to 375 degrees Fahrenheit. Grease a 9 x 13-inch pan and set it aside. In a large mixing bowl, combine 2 ½ cups all-purpose flour, ½ teaspoon baking powder and ½ teaspoon salt, then set it aside.
In a stand mixer or with beaters, cream together ½ cup butter and 1 cup granulated sugar until fluffy, about 3 minutes. Combine 1 large egg, 1 egg white, 1 ½ tablespoons sour cream, and 1 teaspoon vanilla extract. Mix together until fully incorporated. Add the dry ingredients until all is fully combined.
Gently press the dough into the bottom of your 9 x 13-inch pan. Bake for 17-20 minutes until the edges are lightly golden and a toothpick inserted in the center is clean. Let them completely cool before frosting.
To make the frosting, whip together ¼ cup unsalted butter, 2 cups powdered sugar, and 2-3 tablespoons half and half until fluffy. Add ½ teaspoon vanilla. Add any color of food coloring if using. Spread on top of the cooled bars.
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Updated on May 9, 2021Originally Posted on May 18, 2014