Melt coffee in hot water while stirring. Allow to cool.
Mix flour, sugar, and salt in a bowl.
Add egg, cubed butter, and coffee.
Knead with your fingertips until the dough is firm and smooth.
Wrap in plastic film and let rest in the refrigerator for 2 hours.
Preheat the oven to 180C degrees (356F).
Roll out the shortcrust pastry between two sheets of baking paper with a rolling pin to a height of about 3 mm.
Lay the base in the baking pan, resting the side with the baking paper on the bottom; prick the pastry with the tines of a fork.
Cover the dough with baking paper. It has to adhere to the base and edges of the dough, then spread a layer of dried beans on the bottom for baking the tart without filling. This way, the shortcrust pastry will not puff up during baking.
Remove from the oven, discard the hot beans carefully, and let cool completely before stuffing.