For the crust:
For the filling:
1. In a food processor process flour, powdered sugar, salt and cold cubed butter. process until crumps are formed. Add egg, process until dough is formed.
2. Transfer the dough to a work surface, pat into a ball and flatten into a disk. Wrap in plastic and refrigerate for 1 hour.
3. Roll out the dough on a lightly floured board. Lightly dust the top of the dough or the rolling pin with flour as needed. roll until the dough is about 1/8 inch thick.
4. Transfer the dough to a 9-10-inch (24-25cm) tart pan. evenly press the pastry onto the bottom and up the sides of your pan. Trim off the excess dough off the top of the tart pan. Gently pierce the bottom of the crust with the tines of a fork. Transfer to the freezer for 30 minutes.
5. Preheat oven to 360F/180C.
6. line a parchment paper over the dough. Fill with dry beans, rice or pie weights. Bake for 15 min. Remove the weights and the parchment paper. Return to oven for another 10 minutes or until crust is golden brown. Let cool.
7. In a medium size bowl place chopped chocolate and butter. In a small saucepan bring to a simmer heavy cream and pure the cream over the chocolate and let sit 1 minute. Stir until smooth. Pour immediately the filling into the tart and leave to set overnight in room temperature or 3-4 hours in the refrigerator.