Hazelnut Mocha Tart

3 tablespoons butter
1 1/2 cups (7oz.) blanched whole hazelnuts
6 tablespoons sugar
3 1/2 oz dark chocolate, plus more for decoration
3 1/2 oz milk chocolate
4 tablespoons freshly brewed strong espresso
1 large, beaten egg
1 1/4 cups (10 fluid ounces) heavy cream

Lightly butter the ring of a 7-inch springform pan (you only need the ring part of the pan to keep the ingredients together as they firm up in the fridge, you won't be using the bottom part of the pan). Butter a serving platter or cake stand that is wide enough to hold the ring, and place the ring on the platter.

In a food processor, combine the hazelnuts and 4 tablespoons of the sugar and process until the mixture resembles coarse sand. Add 2 tablespoons of the butter and process until combined. Press this mixture firmly and evenly onto the serving plate, within the borders of the springform ring, and set aside.

Put the dark and milk chocolates in a small bowl and melt them, either in a microwave oven or over a saucepan of gently simmering water. Add the espresso and stir until well combined. Beat in the egg and the remaining 1 tablespoon butter and stir to combine. Let cool to room temperature.

In a large bowl, using a whisk or an electric mixer, beat the cream, and remaining 2 tablespoons sugar until firm peaks form. Fold the whipped cream into the chocolate mixture and spoon the mixture over the hazelnut crust. Refrigerate until firm, at least 5 hours. When ready to serve, remove the springform ring and garnish with grated dark chocolate.