This cake is moist and extra fluffy without being overly sweet. I usually reserve this recipe for summer when fresh strawberries are in season. Many households in Japan serve this cake at Christmas even though not all celebrate the occasion. You can choose to use a different type of fruit other than strawberries, but in Japan, the red of the strawberry is believed to repel evil spirits.
Preheat the oven to 350°F. Grease an eight-inch circular cake pan and lightly dust with Bisquick.
Using an electric mixer, combine three-quarters of a cup of sugar with four egg whites, and beat until stiff and glossy.
Add four egg yolks to the egg white mixture, beating until the yolks are incorporated.
Add three tablespoons of milk, one teaspoon of vanilla extract, and one and one-half cups of Bisquick to the eggs and gently mix them into the batter with a spatula. Fold in the melted butter until it is well combined.
Pour the batter into the prepared pan, and bake for thirty minutes or until done. (Insert a toothpick into the middle of the cake and if it comes out clean, then you know the cake is done). Let the cake cool completely on a wire rack.
Whipped Cream Frosting
Add four teaspoons of cold water to a small saucepan. Sprinkle one teaspoon of unflavored gelatin over the water and let stand for 5 minutes, without stirring.
Place the saucepan over low heat, stirring until the gelatin dissolves. Remove the saucepan from the heat and cool to room temperature.
In a mixing bowl, using an electric mixer, combine one cup of heavy whipping cream, one-quarter cup of confectioners’ sugar, and one teaspoon of vanilla extract. Beat until slightly thickened and gradually pour the gelatin into the whipped cream mixture. Whip the mixture until stiff.
Combine one-quarter cup each of granulated sugar and water in a saucepan over medium-high heat. Bring the water to a boil and stir until the sugar has dissolved. Remove from the heat and allow to cool.
Reserve ten strawberries for decorating the cake. Slice the remainders into thin slices.
Slice the sponge cake into 2 layers.
Place one layer on a serving plate and lightly brush the surface with the simple syrup.
Spread a thin layer of whipped cream over the cake layer and arrange the strawberry slices on top. Top with another layer of whipped cream. Place the second layer over the first layer and brush the cut-side with the simple syrup. Spread the remaining whipped cream on top and sides of the cake. Garnish with the reserved strawberries.