Sift the flour into a bowl with the baking powder, salt, and sugar. Add the cold margarine and rub it into the flour until crumbly. Pour in the cold milk, add the egg white, and knead the dough. Let it rest on the counter for 10 minutes.

Pinch off a piece of dough and roll it out into a thin rectangular sheet. Spread with butter and sprinkle with sugar and cinnamon. Cut lengthwise slits into the sheet, stopping short of the edge.

Roll the sheet up into a log.

Twist the log into a ring and pinch the ends together.

Arrange the rolls on parchment paper, brush with egg yolk, and sprinkle with poppy seeds, nuts, or decorative sprinkles. Bake for 30 minutes at 180°C.

Let the finished rolls cool and serve. Enjoy!