2 1/2 cups sifted cake flour
2 1/2 teaspoons baking powder
1/2 teaspoon salt
1/2 cup butter
1 tablespoon lemon zest (grated lemon peel)
1 3/4 cups white sugar
6 egg yolks
1 1/8 cups milk
Line bottom of two 9 inch round pans with parchment paper. Preheat oven to 350 degrees F (175 degrees C).
Measure sifted flour, baking powder, and salt; sift together three times.
Cream butter and lemon zest together. Gradually add sugar, creaming until light and fluffy. Add egg yolks one at a time, beating thoroughly after each addition. Add sifted ingredients alternately with milk to the creamed mixture, a small amount at a time; beat after each addition until smooth.
Bake for 30 to 40 minutes. Cool on wire racks.