White Sheet Cake

Directions

1. 1
   Preheat oven to 350 degrees.
2. 2
   Butter and flour a 12-by-18-by-1-inch rimmed baking sheet, tapping out any excess flour; set aside.
3. 3
   In a medium bowl, sift together flour, baking powder, and salt; set aside.
4. 4
   In the bowl of an electric mixer fitted with the paddle attachment, beat butter and 2 cups sugar until light and fluffy, 3 to 4 minutes, scraping down sides of the bowl as needed.
5. 5
   Beat in vanilla.
6. 6
   With mixer on low speed, add flour mixture in three parts, alternating with the milk and beginning and ending with the flour; beat until just combined.
7. 7
   Transfer mixture to a large bowl; set aside.
8. 8
   In the clean bowl of an electric mixer fitted with the whisk attachment, beat egg whites on low speed until foamy.
9. 9
   With mixer running, gradually add remaining 1/4 cup sugar; beat on high speed until stiff, glossy peaks form, about 4 minutes.
10. 10
    Do not overbeat.
11. 11
    Gently fold a third of the egg-white mixture into the butter-flour mixture until combined.
12. 12
    Gently fold in remaining egg-white mixture.
13. 13
    Transfer batter to prepared baking sheet and smooth batter evenly with a spatula or back of a spoon.
14. 14
    Transfer to oven and bake until a cake tester inserted in the center comes out clean, about 35 minutes.
15. 15
    Transfer to a wire rack and let cool 10 minutes.
16. 16
    Invert cake onto rack, then reinvert and let cool completely.