Preheat oven to 320°F (160°C). Line baking sheets with parchment paper.

Cut the butter into small cubes and rub it into the flour and salt (or use a pastry cutter). Dissolve the yeast in the milk and stir in the egg yolks and 2 teaspoons of the powdered sugar then add to the flour and butter and knead everything together until a smooth dough forms. Beat the egg whites with the remaining powdered sugar until stiff.

Divide the dough into three pieces and roll out each of these on a well-floured surface into ⅛ inch (3 mm) thick rectangles. Spread rectangles with the meringue then sprinkle with the nuts. Roll the rectangles lengthwise into a strudel (like a Swiss cake roll). Using a round cookie/doughnut cutter or a drinking glass, cut crescents (half-moons) from the dough rolls and place these on the prepared baking sheets.

Bake for 15-20 minutes until lightly browned. Cool completely and dust with powdered sugar if desired. Cookies keep well stored in an airtight container or cookie tin.