To make brittle:
To make mousse:
In a medium saucepan over medium-low heat, cook the nuts and sugar, stirring occasionally (more frequently toward the end) until well caramelized and deeply colored. Remove from heat and let cool on a plate.
Combine egg yolks and white sugar and beat with a mixer about 10 minutes, until thick and pale golden. Set aside.
In a clean bowl, beat the egg whites and confectioners sugar until stiff peaks form. Set aside.
In a clean bowl, beat the cream until soft peaks form.
Break up the cooled brittle, then fold into the whipped cream. Once combined, stir in the yolk mixture. Finally, gently fold in the egg whites, then spoon into a mold and rap bottom on work surface several times to get rid of any air bubbles. Freeze at least 8 hours or overnight. To unmold, dip bottom of mold in warm water then invert over a serving platter.