How to make
Sift the flour into a deep bowl and put the egg yolks, sugar and butter inside.
Knead the dough and form a ball, wrap it in cling film and leave it in the refrigerator for 30 minutes to harden.
Roll out a crust as thick as you want your cookies to be. Do it carefully because the dough is crumbly.
Cut out hearts with molds. If you have another, smaller heart mold, cut heart holes in the middle of half of them.
Bake at 180°C in a preheated oven for 12 minutes or until they're baked, because if they are thinner, 10 minutes is enough.
After taking them out of the oven, let them cool slightly without touching them, because they will still be soft and may break. Then they harden and there is no problem.
Place a spoonful of jam on top of the whole hearts and stick the heart with a hole on top.
Decorate them as you like and with what you have.