In a bowl, beat the sugar and egg yolks for 2 minutes, until the mixture whitens. Whisk in the hot cream. Add the chocolate and allow to melt for 1 minute without stirring. With a whisk, stir until the mixture is smooth.
Cover and refrigerate for about 45 minutes, until the ganache is chilled.
Meanwhile, in another bowl, whisk the remaining cream until soft peaks form. Remove the ganache from the refrigerator and, using a spatula, fold in the whipped cream. Divide into 12 small cups or ramekins. Cover with plastic wrap and refrigerate while preparing the white chocolate topping.
White Chocolate Topping
In a small saucepan, bring the cream to a boil. Remove from the heat and add the white chocolate. Allow to melt for 1 minute without stirring. With a whisk, stir until the mixture is smooth, and then stir in the egg yolk. Pour the cream into a bowl. Cover and refrigerate about 30 minutes.
Just before serving, whip the white chocolate topping with an electric mixer for about 2 minutes or until it has the texture of soft meringue.
Top off each cup with a dollop of white chocolate topping, dust with cocoa and garnish with chocolate curls.