Plain Sponge Cake Recipe

Put egg yolks into large mixing bowl and beat until so thick that it is difficult to turn the beater (at least 5 minutes).
Stir in 3/4 cup of the sugar in several portions, combining thoroughly; then beat again until very thick.
Add 1/3 of the boiling water, beat about half a minute; then add another 1/3, beat again; then remainder, beating again.
Set in refrigerator 10 minutes.
Sift flour, measure, and resift 3 times with rest of the sugar.
Sift cream of tartar and salt over egg whites and beat until stiff but not dry.
Now beat the egg yolk mixture again for 2 minutes, and fold in the flour mixture until smooth.
Stir in flavorings and add beaten egg whites, cutting and folding until well mixed.
Turn into an ungreased 10-inch tube pan, and bake in a moderately slow oven (325° F.) for 1 hour, or until it springs back when lightly touched.
Remove from oven, invert, and let stand on tube, not on cake surface, until thoroughly cooled.
Loosen sides and around tube with a thin-bladed knife and remove from pan.
Frost if desired.