Pre-heat the oven to 350F
Cream the Butter: In a large bowl using a hand-held or stand mixer fitted with a paddle attachment, beat the soften butter
Add granulated sugar, brown sugar, vanilla extract and espresso powder
Beat the mixture about 3 minutes until it gets crumbly. Scrape down the sides and bottom of the bowl as needed.
Add the egg yolk and beat agin until incorporated
Add dry Ingredients: Add flour, cocoa powder, baking soda, baking powder and salt. Mix until it forms into a dough.
Add coffee or milk to slightly loosen the cookie dough
Add Chocolate: Add chocolate chunks and M&M and mix until distributed. Add milk or espresso to slightly thin out the batter.
Divide the cookie dough into four (4) portions
Shape: Shape the cookie dough into balls
Roll in chopped M&M
Chill: The cookie dough will be slightly sticky. Cover dough with plastic wrap and chill for 30 minutes while you pre-heat the oven.
Bake at 350F for 13 - 15 minutes.
Let Cool on the pan.
Make it Triple Chocolate: Once the cookie is completely cooled, drizzle melted chocolate on top. You can use semi-sweet, dark or even white chocolate.