A crispy crust made from ice-cream cones is the perfect complement to velvety chocolate mousse.
Make crust: Preheat oven to 325 degrees. In a food processor, combine cones, salt, and sugar; process until fine crumbs form. With machine running, slowly pour butter through feed tube and process until mixture resembles wet sand. Press crumbs in bottom and up side of a 9-inch fluted tart pan with a removable bottom. Bake until crust is golden brown and set, 25 minutes. Let cool completely in pan on a wire rack.
Meanwhile, make topping: In a small saucepan, combine hazelnuts, granulated sugar, salt, and 1/4 cup water. Bring to a boil; cook 1 minute. Strain hazelnuts and spread in a single layer on a parchment-lined baking sheet. Bake until nuts are toasted and shiny, 15 minutes. Let cool completely.
Make filling: In a medium saucepan, bring 3/4 cup cream to a simmer; remove from heat and add chocolate. Let stand 5 minutes; whisk to combine, then let cool to room temperature. In a large bowl, whip 1 cup cream with confectioners' sugar until stiff peaks form. Gently fold in chocolate mixture until combined. Pour filling into cooled crust and refrigerate until chilled and completely set, about 1 1/2 hours (or wrap tightly with plastic and refrigerate, up to 2 days). To serve, top tart with hazelnuts.
If you can't find peeled hazelnuts, use unpeeled (they will be quite dark when roasted).