Sugar-free Italian Sponge Cake Recipe

Preheat oven to 325 degrees F. Grease a 9-inch layer cake pan. Place egg yolks and sugar substitute in bowl. Beat with electric mixer until well blended. Add vanilla and lemon rind. Continue to beat and gradually add the soy powder 1 tablespoon at a time. Beat until well blended. Stir in heavy cream. *Beat egg whites with cream of tartar until stiff. Fold yolk mixture into whites with an under and over movement. Be careful not to break down egg whites. Turn into prepared cake pan and bake about 30 minutes, or until cake tests down.