¾ cup (1½ sticks) unsalted butter, softened at room temperature
Instructions
Pre-heat oven to 350 degrees; spray a 9x13 pan with cooking spray and set aside
In a medium bowl, whisk together milk, egg whites, vanilla and food coloring; set aside
In the large bowl of an electric mixer, whisk together flour, sugar, baking powder and salt; add butter and beat on low speed until all of the ingredients are in wet lumps
Add half of milk mixture and beat on medium speed for 1-2 minutes or just until combined; scrape the sides of the bowl with a spatula and then add remaining milk mixture; beat on medium speed just until combined without overmixing
Pour batter into prepared pan and bake 25-35 minutes or until a knife comes out clean from center