1.In a bowl, cream butter, sugar and egg yolks together. Mix in flour a little bit at a time until a soft dough forms. Roll dough into 1 inch balls. Place balls 2 inches apart onto a baking tray. Use your finger to make a well in the center of each cookie and fill with jam.

2.Bake for 10 to 12 minutes in the preheated oven(190 degree), until golden brown on the bottom. Remove from cookies to cool on wire racks.