Cream the room temperature butter with the powdered sugar and salt (can use a whisk or a mixer with a paddle attachment).
Add the egg and mix very well until smooth.
Whisk together the flour and baking powder.
Add the flour mixture to the butter mixture and quickly mix with a spatula or by hand until homogeneous.
Take ⅓ of the dough and make it chocolate. For this, mix the cocoa with the milk and add it to the dough. Knead well until the entire dough is a uniform color. Then put it in a bag in the freezer for 30 minutes.
Carefully roll out the vanilla dough between two sheets of parchment paper into a rectangular sheet, and from the chocolate dough, pinch off pieces of different sizes and scatter them randomly over the surface so that they form spots. Roll it out again until everything is combined.
Cut out the cookies using a cookie cutter, trying to fit as many cookies as possible so you don't have to re-roll the dough.
Preheat the oven to 165°C and bake for ~10 minutes until the edges start to turn golden.
Let cool and enjoy with milk!
