German Black White Cookies

250g soft butter
250g sugar (I use feinster Backzucker)
1 pack vanilla sugar
1 egg yolk, 1 whole egg
2 T rum
500g flour (I use type 550)
2 T cocoa
1 egg white, lightly beaten, for brushing

Cream butter, sugar, vanilla sugar, egg & egg yolk. Add rum. Add flour a little at a time and continue to beat until mixed, then turn onto counter and knead into a smooth dough. Separate into 2 halves. Mix the cocoa into one half of the dough, kneading until uniformly brown. Wrap each ball of dough in plastic wrap and chill.

Roll out the dough in sections, layering to create different patterns (see the picture for ideas). Brush each layer with beaten egg white before adding the next layer. Roll into logs, wrap in plastic wrap and chill.

Preheat oven to 190°C (375°F). Slice cookies from the log about 1cm thick and bake for 10-12 minutes on a parchment-lined baking sheet.  The white part should not brown.