To toast and skin hazelnuts:
Spread the nuts in a single loose layer on a rimmed baking sheet. Bake in a preheated oven at 350° F for 15 to 20 minutes, stirring and checking the nuts from time to time, until they are golden brown inside when you bite or cut them in half. Let the nuts cool completely (there is no advantage to wrapping them in a towel or bag to “steam” as is widely believed). When cool, rub the nuts together with your hands or in a dishtowel or pour them into a coarse mesh strainer and rub them against the mesh until as much skin flakes off as will come off. Do the best you can; some skins will always remain.
Put 1 cup (140 grams) of the hazelnuts in the blender—a Vitamix is even better—and set the remaining handful of nuts aside for garnish. Process the nuts to the smoothest possible paste, scraping the container as necessary. In a Vitamix, the nut paste will become very liquid.
In a medium bowl, mash and mix the cream cheese and liqueur together (or whisk the liqueur with the mascarpone) until blended. Dump the chopped chocolate on top. Set aside
With an instant-read thermometer handy, heat the milk, sugar, salt, and nut paste in a heavy medium saucepan until steaming hot. Meanwhile, whisk the eggs in a medium bowl to blend yolks and whites thoroughly. Gradually whisk about half of the hot milk mixture into the eggs. Scrape the mixture back into the saucepan and cook over low heat—stirring constantly and scraping the bottom, sides, and corners of the pot to avoid scrambled eggs—until the mixture is slightly thickened and registers about 165° F on the thermometer.
Immediately scrape the egg mixture over the chocolate mixture. Stir until the chocolate is completely melted and the mixture is smooth. Refrigerate for about 45 minutes, or set in a bowl of ice and water for 8 to 10 minutes, stirring and scraping the sides from time to time, until the mixture is cool but not congealed.
Whip the crème fraîche until it begins to stiffen and hold a shape—but it shouldn't be too stiff. Scrape it into the chocolate mixture and fold until thoroughly blended. Pour the mousse into individual dishes and chill at least several hours or overnight for the best flavor and texture, or up to 2 days. Chop the reserved nuts and sprinkle over the mousses before serving.
My career was sparked by a single bite of a chocolate truffle, made by my Paris landlady in 1972. I returned home to open this country’s first chocolate bakery and dessert shop, Cocolat, and I am often “blamed” for introducing chocolate truffles to America. Today I am the James Beard Foundation and IACP award-winning author of ten cookbooks, teach a chocolate dessert class on Craftsy.com, and work with some of the world’s best chocolate companies. In 2018, I won the IACP Award for Best Food-Focused Column (this one!).