In a large bowl, stir together the flour, white sugar, baking powder, aniseed and salt. Add the butter and rub in with your fingertips until the mixture resembles breadcrumbs. Add the lemon zest, fold in the beaten egg and liqueur, and knead briefly until the dough is smooth. For the dough into a ball, cover with plastic wrap and let rest in the fridge for 30 minute.
Preheat the oven to 350 F. Grease an 8 inch tart pan with butter, olive oil or cooking spray.
On a floured surface, roll out the dough and line the tart pan, cutting and patching the dough if it tears. Prick the base all over with the tines of a fork and press the dough into the walls of the pan.
To make the filling, in a small bowl, break up the queso fresco with a fork into a coarse mash. In a medium bowl, beat the eggs with white sugar, then add the cheese and chopped mint, mixing to combine.
Pour the filling into the prepared pastry shell. Bake in the oven until firm and lightly browned on top, approximately 50 minutes.
Transfer the pan to a wire rack and let cool. Decorate with mint leaves.