Make the crust: 

1. Combine the flour, cocoa powder, baking powder and salt in the bowl of a food processor.  Pulse briefly to mix the ingredients.  Cut the cold butter into approximately ½ inch cubes and add to the processor bowl.  Pulse until it forms a crumbly mixture.  Add in the egg, egg yolk and vanilla and process until the dough begins to form a ball.  (No food processor? No problem! Just combine the dry ingredients together in a medium bowl. Add in the cubes of butter, egg, egg yolk and vanilla. Cut the butter into the mixture using a pastry scraper or spatula until rough crumbs form.  Knead the dough until all the ingredients are absorbed and forms a ball.)
2. Transfer the dough to a lightly floured work surface and work into a ball. Wrap the dough tightly in a sheet of plastic wrap and let rest in the refrigerator until well chilled, 30 minutes – 1 hour. 
3. Butter and flour a 10″-diameter tart pan with removable bottom.
4. Preheat the oven to 350 degrees Fahrenheit. 
5. Remove the dough from the fridge and lightly dust a work surface with flour. (Alternatively, roll out between 2 sheets of parchment or waxed paper.) Roll out the dough to about ½ inch thickness. Using the rolling pin or the paper, carefully pick up the pastry and lay it over the prepared pan. Tuck the pastry into the pan. Roll the rolling pin over the top to cut any stray edges.  Prick the base all over with a fork. 
6. Cover with a piece of parchment paper; fill the parchment paper with drief beans or baking weights and bake for 20 minutes.  Remove the paper and weights. Bake for another 5 minutes or until firm and dry to the touch.  Remove crostata from oven and allow to cool completely. 

Make the filling: 

1. Bring the cream just to a boil in a small saucepan. Remove from heat. Add in the chopped chocolate. Let sit for about 1 minute. Stir with a whisk slowly until the chocolate is melted and smooth. Let it sit until it has reached a slightly thickened consistency, stirring occasionally, about 10-15 minutes.
2. Pour the filling into the baked crust. Smooth out the top with a spoon. Sprinkle with flaky sea salt. Place in fridge for at least 2 hours, or until firm.  When ready to serve, remove from fridge and sprinkle with additional flaky sea salt.  Buon appetito!