Preheat oven to 230°F. Cover two cookie sheets with parchment paper trimmed to fit perfectly on the pan bottom. Take an 8 x 2 1/2 -inch high dessert or flan ring (no bottom) and trace three circles on the parchments. Turn the papers over and place on your cookie sheets. Set aside.
To make the meringue: In the bowl of an electric mixer, beat the egg whites on medium-high speed until you have soft peaks. Turn the mixer to low and add the granulated sugar, a tablespoon at a time, waiting until each addition is mixed in before the next addition. Turn the speed up to high and beat another minute. Sift the confectioners' sugar into the egg whites. Turn the machine to low and mix briefly to combine.
Fit a pastry bag with a 1/4-inch round tip. Fill with the meringue batter. Starting from the center of the drawn circles, squeeze out spirals until your circle is about 1/2 an inch smaller than the drawn circle. If you do not have a pastry bag, use a silicone spatula to shape three circles of meringue batter.
Squeeze out any leftover batter into small circles, about an inch wide, and then lift up, like Hershey's kisses, to decorate the cake later, if desired. Place in the oven, turn down the temperature to 220°F and bake for two hours. Turn off the oven and let the meringues remain in the oven another two hours to dry out. May be made two days in advance and stored uncovered at room temperature.
To make the sauce, place the raspberries into the bowl of a food processor fitted with a metal blade and purée, scraping down the sides of the bowl until all the fruit pieces are puréed. Add the water and sugar and mix.
Taste and add more sugar if the mixture is too tart. Use a sieve to strain out the seeds and discard. May be made two days in advance and stored covered in the fridge.
To make the mousse: Melt the white chocolate either in a double boiler or in the microwave oven for 45 seconds, stir, 30 seconds, stir, and 15, seconds, stir, until melted and smooth. Add the egg yolks one at a time and whisk well. In a large bowl, with an electric mixer on high speed, beat the whipping cream until stiff. Fold the whipped cream into the white chocolate mixture and mix until well blended.
To assemble the cake, you will need an 8-inch cardboard circle. If the circle is larger than your ring, trace your ring and then cut out the circle. Line a cookie sheet with parchment paper, place the ring on top, and place the cardboard circle into the ring. Place a tablespoon of the mousse on the cardboard to glue the meringue circle in place. Place one of the meringue circles in the ring. Pour a third of the mouse into the ring to cover the meringue. Make sure you get some mousse on the sides between the meringue and the ring. Add the second meringue circle and another 1/3 of the mousse. Repeat with the last meringue circle and more mousse and then use a metal flat blade spatula to smooth the top, reserving any extra mousse in a small bowl in the refrigerator to decorate the top, if desired.
Place into the freezer for four hours or overnight.
Remove from the freezer. To remove the ring, place the cake (with the cardboard bottom) on top of a large can of tomatoes or vegetables. Place boiling water in a small bowl. Take a towel or paper towel, dip it into the hot water, and then rub around the outside of the ring; this will help release the ring from the mousse. Go around the entire ring with the hot towel. Take your hands and gently slide the ring down off the cake. Place the cake on the parchment-lined cookie sheet.
To decorate the cake, use a vegetable peeler to scrape white chocolate curls on top of the cake or use any leftover mousse in a pastry bag with a decorative tip. Store cake in the freezer and then remove five minutes before serving to cut perfect slices. To serve, spoon some raspberry sauce on your serving plate and place the cake slice on top. Store in the freezer for up to three months.