In the bowl of a stand mixer, cream the butter and sugar together.
Add the milk, food colouring and egg and mix together well.
Add the flour, cocoa and baking powder and mix thoroughly.
Cover the finished dough with cling film and leave in the refrigerator for 2 hours. After 1 hour 45, preheat your oven to 190 º C.
Take out the chilled dough, roll small balls out of it, roll them in powdered sugar and put on a baking sheet.
Bake the cookies for about 15 minutes until done.