Preheat the oven to 350 degrees F (175 degrees C). Grease a 10-inch cake pan.

Beat egg whites and cream of tartar until soft peaks form. Add 3/4 cup sugar gradually, beating until very stiff.

Cream butter and 1 cup sugar in a large bowl with an electric beater until light in color. Add egg yolks, and beat until thick and fluffy. Sift flour, baking powder, and salt over batter; fold in. Gently fold in egg whites. Pour batter into prepared pan.

Bake in the preheated oven until a toothpick inserted into the center comes out clean, about 50 to 60 minutes. Cool in the pans for 10 minutes, then remove to a wire rack to cool completely.