1. Chop white chocolate into small pieces and melt gently over a double boiler or in the microwave, stirring until smooth. Let cool slightly. In a chilled bowl, whip the heavy cream until soft peaks form. Keep chilled. In another bowl, beat egg whites until foamy, then add sugar gradually and beat until stiff peaks form. Gently fold whipped cream into cooled white chocolate until combined. Then fold in egg whites carefully to keep mixture light. Spoon or pipe mousse into baked and cooled tartlet shells. Smooth or swirl tops as desired. Chill tartlets in refrigerator for at least 1 hour to set. Garnish before serving.