Cut two layers from the sponge cake that are about 3/4-inch thick each. Place one cake layer in the bottom of an 8-inch round springform pan. Choose 10 strawberries that are of equal height (you may need more or less depending on size). Cut them in half vertically and arrange them pointed sides up around the edge of the pan. They should be snug against the side of the springform pan. Arrange the remaining whole berries, pointed ends up, on top of the cake. Make sure they are close together to fully cover the cake. Melt the white chocolate and water in a double boiler over simmering (not boiling) water. Stir constantly until the chocolate is smooth. Remove from the heat and let cool to 85 degrees F. When the chocolate is cooled, whip the heavy cream until soft (not stiff) peaks form. Gently fold the whipped cream into the chocolate mixture. Gently spread the mouse over the berries in the pan (reserve about 3/4 cup of the mousse for the top layer). Use a spatula to carefully push it into the nooks and crannies so the sides of the pan are filled with mousse between the berries. Smooth the top so it is even. Top the mouse with the remaining cake layer and gently press down so it is even. Spread the reserved mousse over the top of the cake layer (it will be a thin coating). Cover the cake and place in the refrigerator for 4 hours or until the mousse is set. To serve: Moisten a dish towel with hot water and wrap it around the outside of the springform pan and let sit for 2-3 minutes. Carefully remove the sides of the pan. You can smooth the sides and top as needed with a dry, warm metal spatula.