Mix the softened butter, sugar, and vanilla for about 4 minutes until the butter is a bit paler. Use a mixer to make it easier.
Add the egg, milk, cacao powder, and red food coloring and mix until you get a homogeneous batter.
Slowly, add the flour and mix until everything is blended and the dough has the right consistency.
Lastly, add half of the white chocolate chips and mix with a spatula.
Make balls and take them to the fridge for 1 hour.
Preheat the oven to 180º (350ºF)
Bake the cookies for 9 - 11 minutes. Let them cool on a rack and, while they are warm, press the rest of the white chocolate chips against the top of the cookies so they stay as decoration.