Sift the flour, baking powder, and powdered sugar into a bowl. This helps prevent lumps in the dough.
375 g flour, 120 g powdered sugar , 1 teaspoons baking powder
Add in butter, salt, and vanilla extract. Knead with both hands until you achieve a smooth dough.
250 g butter, 1 teaspoon vanilla extract , 1 pinch salt
Half the dough. Add the cocoa to one-half and knead until it is absorbed.
1 tablespoon cocoa powder
Divide the white and the brown dough into four equal-sized balls each.
2 tablespoon granulated sugar
Take one of each and knead together until you achieve a nice marble pattern. Repeat until you have four equally sized marbled balls. Now combine them into one big roll which has a (Ø 5 cm/ 2 inch)
Coat the roll in granulated sugar before wrapping it in cling film and leave it to rest in the fridge for around 1 hour. The butter will firm up again, making it easier to cut later.
2 tablespoon granulated sugar, 250 g butter
Cut the cookies
In the meantime, preheat the oven to 160°C/ 320°F circulated heat, 180°C/ 356°F top to bottom heat.
Slice the roll into little biscuits, just less than 0.5 cm/quarter-inch thick, and place onto a tray lined with some baking paper
Bake for around 10-12 minutes. They will be a little soft when you remove them from the oven, but they will harden once cool.
Notes
They should keep in an airtight container up to three weeks.