We start by making the cookie dough for this we beat with a mixer butter and sugar for three minutes. We add the beaten egg and the vanilla extract, beat to add them to the dough.
We are pouring the flour into the blender by tablespoons, waiting for it to integrate before adding the next one, until some crumbs are formed, at which point we add the milk to bind the dough a little. Form a ball. Spread between two kitchen papers a piece of the dough with a thickness of about 5 mm and cut large hearts and then in the middle of the cookies, cutting a smaller heart that we also bake as small pastries. Repeat this operation until finished.
Go to a baking tray and leave to cool in the fridge for fifteen minutes. Preheat the oven to 180ºC. Bake for 15 minutes. Once outside, let them rest for five minutes on the tray and transfer them to a rack until they cool completely.
To decorate them, we will have to heat for half a minute the jam in a saucepan. If it has many pieces, pass the blender until it is very smooth and put it in a kitchen bottle.
Spread a little jam on a closed cookie, place another one with the small cut-out heart and gently press so that they stick together. Sprinkle with icing sugar and fill with a bottle or pastry bag until the cookie is covered by the jam. Let them rest until the jam solidifies.