Black and White Cookies
Combine the flour, sugar, butter, vanilla sugar and egg yolks. Knead to form a smooth dough. Divide the dough in half and knead the cocoa powder into one half, and the cream into the other half. Wrap each dough in plastic wrap and refrigerate for at least 2 hours.
On a floured work surface, roll each dough out to about 1.5 cm (approximately 1/2 inch) thick. Cut each into (2) 1.5 cm (approximately 1/2 inch) wide strips. Gently press the 4 strips of dough together to form a checkerboard pattern. Brush the strips with a bit water to help them stick, if needed. Trim the ends, wrap in plastic wrap, and refrigerate for 30 minutes.
Preheat the oven to 180°C (approximately 350°F). Line a baking sheet with parchment paper.
Cut the dough into 2-3 mm (approximately 1/8 inch) thin slices. Place on the prepared baking sheet and bake 10-12 minutes, until golden brown.
Transfer to a wire rack to cool.