For the tart base: In a bowl, add the flour, the butter (in cubes), the egg (beaten), and the salt. Mix all the ingredients together, first using a spatula or knife, later using your hands (add a little bit of water to loosen the mixture if needed). Knead on a surface covered with flour, and make the dough into a ball. Place in the fridge and leave it for three hours. After three hours, roll it flat using a rolling pin. Place the rolled out dough into a tart tin (or muffin tin, for individual tarts), covering the bottom and sides. Cut up any excess dough and pierce the dough in several places using a fork. Preheat the oven to 200° C. Place a piece of parchment paper onto the dough and spread beans onto it (this is to prevent the douch from becoming uneven). Bake the tart for 20 min.
Cut the pumpkin flesh into pieces and boil for about 25 minutes until soft. Turn the pumpkin pieces into a mash using a blender. Add the rest of the ingredients for the filling and empty onto the tart base. Bake in a preheated oven for 40 minutes, at 180° C.
Serve with whipped cream.