For this recipe, make sure you have all your bowls ready to go. Set up that Mise en Place and rock it!
In a saucepan over medium-low heat, melt the butter with the white chocolate, stirring constantly. Set aside.
Whisk the yolks, sugar, and Frangelico in the bowl for the top of the double boiler until pale, yellow and thick. Whisk it good. Set it over the double boiler, with just simmering water, and cook until very thick, about 3 minutes. Test to see if it coats the back of a spoon. Remove from heat and spoon into a large bowl.
Whisk the white chocolate into the egg mixture.
In a clean bowl, whisk the heavy cream over high speed until stiff peaks form.
In another clean bowl, with whisk attachment, beat the egg whites with the cream of tartar until stiff, but not dry, peaks form.
Gently fold the cream and egg whites into the white chocolate mixture. Refrigerate for at least 3 hours to set before serving.
The instructions said to spoon into goblets, and you can bet your cute behind, I was bummed to discovered I owned not one goblet. I will be remedying that for future mousse consumption. We should all own a good goblet or two.
Dust with cocoa powder or chocolate shavings if desired.