Step 2: making the pastry
If you have your own butter pastry recipe feel free to use it if not here is a simple one.
Butter dough recipe:
250g butter (room temperature )
3 tsp vanilla sugar
1 egg yolk
2 spoons rum or backing flavor (rum, butter rum, what you want)
Stir everything together.
Screen the flour on the butter sugar mix while kneading butter-sugar-stuff.
Further you need some spoons of cacao powder to color a part of the pastry.
In case of the the example picture the black and white ratio is roughly 50:50 so color have of the dough with cacao nicely dark brown. 4 to 5 spoons should make it don't use to much or the dough will get to dry , knead it well the color will adjust.
Now form bowls two bowls, put foile arround it and put the dough at least 4 hours in the fridge.