1

Preheat the oven to 350°F. Butter and flour one or two 9-inch cake pans. In a bowl, sift together the flour, baking powder, and salt and whisk to combine. Cream the butter and the 3/4 cup sugar using a heavy wooden spoon, a handheld mixer, or a stand mixer fitted with the paddle attachment. When the butter softens, switch to a whisk. Continue whisking, for about 5 minutes. Whisk in the egg yolks, one at a time, until the mixture is smooth.

2

Whisk in the milk and vanilla, then the flour mixture, 1/2 cup at a time. Don't overwork. Transfer the egg mixture to a large bowl to make folding easier.

3

Beat the egg whites and cream of tartar (if using) for about 2 minutes, until soft peaks form, then beat in the remaining sugar for about 2 minutes, until medium peaks form. Whisk one-fourth of the egg white mixture into the butter mixture to lighten it.

4

Fold in the rest of the egg white mixture with a rubber spatula. Spread the batter in the cake pans.

5

Bake 1-inch-thick cakes for about 30 minutes or a 2-inch-thick cake for about 40 minutes, or until the cakes bounce back to the touch or until a knife or toothpick inserted in the centers comes out clean. Let cool for 5 minutes in the cake pans and then turn out onto a cake rack.