Put the flour on your worktop and make a hole; add the butter cut into cubes and rub it with the flour with your hands. Add the egg, salt, sugar and vanilla. Work the ingredients together quickly to form a smooth ball. Put it in the fridge for 20 min if you find it a bit sticky. With a rolling pin roll the pastry flat and lay it into a flan baking tray. Pinch the pastry with a fork (or you can put some dry beans on it too avoid the formation of air bubbles). Cook it in a pre-heated oven for 20 min for 190 C. Make the gelatine according to the instructions on the packet or dissolve 2 tbsp of jam with 2 tbsp of hot water and brush it on the tart. You can serve it with cream if you like.