Mix flour and baking powder and sieve into a bowl. Add sugar, vanillin sugar, lemon zest, salt, butter and 3 tablespoons of cold water. First knead with the dough hooks, then with cool hands to a smooth dough. Wrap the dough in foil and chill for at least 1 hour. Cut the dough in half and put one half back in the fridge. Roll out remaining dough on a floured work surface to a thickness of approx. 3 mm, cut out hearts of different sizes (4-7 cm Ø). Place the hearts on two baking trays covered with baking paper.
Bake one after the other in a preheated oven (electric cooker: 200 °C/ convection oven: 175 °C/ gas: level 3) for approx. 10 minutes. Let it cool down on a cake rack. Process the remaining dough in the same way. Sift icing sugar and mix with lemon juice. Colour 1/4 icing pink, 1/4 icing red. Pour each glaze into a freezer bag, cut off a small corner. Decorate the hearts as you like with icing, pearls and crumbles