- In a food processor, blend the hazelnuts, flour and icing sugar to a fine powder. Add the butter and pulse a few times until it forms pea-sized pieces. Add the egg and blend just until the dough starts coming together.
- On a lightly floured surface, knead the dough until smooth. Press the dough evenly and firmly on the bottom and up the sides of an 11-inch (28 cm) tart pan with a removable bottom. With a fork, prick the bottom of the crust. Refrigerate for 30 minutes.
- With the rack in the middle position, preheat the oven to 400°F (200°C).
- Cover the crust with a sheet of foil and fill with dry beans or ceramic pie weights. Bake for 15 minutes or until the crust starts to brown. Remove the beans and foil. Continue baking until the crust is golden brown, about 5 minutes. Let cool completely.
- Place the chocolate in a bowl.
- In a pot off the heat, whisk together the cream, milk, sugar and eggs. Cook over medium-low heat, whisking constantly, until the mixture has thickened slightly. Poor over the chocolate and let melt for 1 minute without stirring. Whisk until smooth. Slowly whisk in the oil. Pour the chocolate cream into the crust. Refrigerate for 3 hours or until the filling is set.
- When ready to serve, with an offset spatula or the back of a spoon, make a decorative pattern in the top of the chocolate cream. Sprinkle with cocoa powder and garnish with the hazelnuts. Let sit at room temperature for 15 minutes before serving.
The higher the cocoa percentage in your chocolate, the stiffer your chocolate cream will be. For this recipe, we preferred the taste and texture when using chocolate with less than 60% cocoa content.