For the linzer trees, put the flour in a mixing bowl. Add cold butter in small pieces, sugar, egg, salt and lemon zest.
Mix with the dough hook of the mixer until you have a smooth shortcrust pastry.
Divide into 2 portions, wrap in plastic wrap and place in the refrigerator for 1 hour.
Preheat the oven to 180 °C convection oven. Roll out the dough in portions on a floured work surface to a thickness of 1-2 mm.
Cut out cookies with any shapes. Place half of the cut cookies on the baking tray.
For the other half, cut out the center first with small shapes and then place on the baking sheet as well. Bake in the oven for 8-10 minutes.
Let cool on a cooling rack. Heat the currant jam, stir until smooth and brush the whole cookies with it.
Place a matching cookie with a hole on top of each one and the Linzer trees are ready.