The base:Cut 150 g butter into smaller pieces.Mix butter, 300 g wheat flour, 100 g powdered sugar, and 1 egg together in a mixer until it begins to come together. Pour the dough out onto the work surface and shape it into a firm dough. Let the dough rest in the fridge for 30 minutes.Sprinkle flour on the work surface and roll out the tart dough. Place the dough in a non-stick tart pan. Chocolate filling:Coarsely chop the chocolate.Melt 200 g butter and 200 g sugar in a saucepan. Once the butter and sugar are melted, pour over the chocolate and add the coffee. Stir everything into a smooth mixture. Fold a tablespoon of wheat flour into the mixture.Mix in the 3 eggs one at a time.Pour the chocolate mixture into the tart pan and bake for 40 minutes at 180 degrees Celsius (356 degrees Fahrenheit) conventional oven.Let the tart cool and optionally decorate with cocoa.