Whisk flour, cocoa powder, baking powder, and salt in a bowl.Beat butter and sugar until light and fluffy.Mix in eggs, milk, vanilla, and food coloring until smooth.Stir dry ingredients into wet mixture until combined.Cover and chill dough for at least 2 hours.Preheat oven to 350°F and line baking sheets.Roll dough into balls and coat generously in powdered sugar.Bake for 10 to 12 minutes until cracked and set.Cool briefly, then transfer to a wire rack to finish cooling.