Mix the softened butter with the sugar then add the vanilla and then stir in the flour.
Mix with your hands until combined very well and makes a large dough ball. Shape cookies into 2cm balls and flatten cookies slightly and place on an ungreased cookie sheet. Indent centers of cookies with your thumb.
Bake in the preheated oven until lightly brown, about 12 minutes. Remove from oven and immediately fill thumbprints with your favourite jam. Remove cookies and cool on wire racks.