Sift the flour, cocoa powder, and powdered sugar into a large bowl. Then, add the butter pieces and salt. Finally, add the egg and knead everything into a smooth dough.
Roll out the shortcrust dough and place it in a 9-inch tart pan. Pull up the edges so that the rim of the pan is slightly covered.
Place a piece of parchment paper on the dough and spread dried beans or pie weights on top to blind bake it. Bake the dough in a preheated oven at 350°F for 15 minutes. Remove the beans or pie weights and bake the crust for another 5 minutes. Let the shortcrust cool.
Wash 2½ cups of the raspberries and boil them with water in a saucepan.
Mix the instant pudding powder and sugar with a little water until smooth.
Stir the mixture into the raspberries until it has thickened.
Let cool briefly and spread the mixture onto the baked shortcrust. Place the tart in the refrigerator for 60 minutes.
Chop the dark chocolate, if you haven't already. Bring the heavy cream to a boil and pour it over the chopped chocolate. Stir the mixture until smooth and let it cool briefly.
Pour the ganache over the raspberry layer and chill the tart for 60 minutes.
Decorate the tart with the remaining fresh raspberries shortly before serving.
