Mix the butter with the sugar until frothy. Separate the eggs. Stir in egg yolk, flavor, salt and flour. Shape the dough into balls and first roll in the egg white then in the nuts.
Place a little space on a baking sheet lined with baking paper. Press a well in the middle of the balls and pour the jam.
Bake in the preheated oven on the middle shelf for about 12 - 15 minutes at 180 degrees.