Combine flour and powdered sugar in a mixing bowl.

Cut the butter into small pieces and add them to the bowl.

Crumb the butter into the flour mixture until the butter resembles grated Parmesan.

Add the egg.

Knead all the ingredients together into a uniform dough. Knead as briefly as possible and stop as soon as the dough is cohesive.

Roll the dough out thinly with a rolling pin to a thickness of about 3 millimeters.

Cut out the cookies with a cookie cutter - you can also use a glass - about 5 centimeters in diameter.

Place the cookies on baking sheets lined with baking paper.

Whisk the egg with a fork in a deep plate.

Sprinkle the cookies with cinnamon sugar.

Bake the cookies for 6-8 minutes at 200 degrees Celsius (392 degrees Fahrenheit) (180 degrees Celsius (356 degrees Fahrenheit) for convection oven).

Let the baked cookies cool on a wire rack.