To make the crust: In a large bowl, mix together the flour, hazelnut meal, powdered sugar, salt, lightly beaten egg and butter. Using a pastry cutter, a large fork or a potato masher, cut the chilled butter into the flour until it resembles oatmeal flakes with a few pea-sized pieces of butter still visible. When a ball forms, turn out onto a well floured surface. Roll the dough out, if making individual tarts divide the dough into 5. If making one large tart, roll out to fit a 9-inch fluted tart pan. Fit the circle in the bottom and up the sides of the pan. Use the tines of a fork to pierce the dough several times and place tart in the freezer for at least 20 minutes.

Place a rack in the upper third of the oven and preheat oven to 350 degrees F. Remove the tart shell from the freezer, bake for 20 - 25 minutes or until the crust just barely starts to turn golden. Remove from the oven and allow tart shell to cool completely before filling.

To make the filling: In a small saucepan set over low-medium heat, bring the cream to just simmering. Remove it from the heat and stir in the chocolate, vanilla and if using, the chili powder. Mix until smooth and the chocolate is completely incorporated. Whisk a small amount of the hot chocolate cream (about 1-2 tablespoons) into the lightly beaten eggs until smooth.

Pour the chocolate filling into the prepared pastry and bake it for 12- 15 minutes (for mini tarts) and 18 - 22 minutes for large tart. If the center jiggles slightly, the tart is done. If the filling starts to crack, remove from the oven immediately so as to not overcook it.
Allow the tart to cool in the pan on a wire rack for 15 minutes. Remove the tart ring and chill in the refrigerator for at least an hour prior to serving.