Mix the butter with sugar, vanilla sugar and salt until creamy. Knead in the egg yolk, flour and nuts. Wrap the dough in foil and put it in the fridge for 2 hours.
Form two rolls of dough. Cut each into 20 slices. Shape it into balls and place them on baking sheets lined with baking paper. Press hollows in with a wooden spoon handle. Bake at 200 ° C on the 2nd rack from the bottom for 10-12 minutes. Let cool down.
Dust with powdered sugar. Stir the nougat over a water bath until smooth and fill the cookies with it.