Preheat the oven to 375°F (190°C).
In a microwave-safe bowl, melt the butter. Add cracker crumbs and sugar and mix thoroughly.
Press mix into an 8-inch (20 cm) round, hinged mould and cook 10 minutes. Set to cool.
Meanwhile, melt chocolate in bain-marie and reserve. Prepare gelatine and reserve.
Whisk egg whites into foam.
Heat yolks with sugar. Add Mascarpone, lukewarm white chocolate and prepared gelatine into yolk mixture. Delicately, incorporate egg whites.
Pour preparation over the crust and refrigerate 3 to 4 hours before serving. Garnish with peeled and seeded citrus sections (suprêmes).