Knead all the dough ingredients well, wrap in foil and place in the refrigerator for approx. 1 hour.
Shape a quarter of the dough into a roll, cut into approx. 12-14 small pieces, shape them into small rolls, bend into an S-shape and place on the side of the work surface until the next step.
Mix the egg yolks with the condensed milk, pour some of the sugar in a soup plate or something similar. Take the S in your hand one after the other, brush with egg yolk and press the coated side into the sugar. Place on a baking sheet lined with baking paper. Ideally, the finished trays should be placed in a cool place, as this will prevent the Butter-S from drifting apart during baking. However, it has no effect on the delicious taste.
Preheat the oven and bake at 190 ° C for about 8-12 minutes until light brown. Store in a can after cooling.