INGREDIENTS
1/2 cup
butter (, softened)
1/2 cup
sugar
1/2 cup
brown sugar
1
egg (, at room temperature)
1 tsp
vanilla extract
1 cup
all-purpose flour
1/2 cup
cocoa powder
1 tsp
baking soda
1/4 tsp
salt
2
Tbls milk
1 cup
mini M&M's (, plus 1/4 cup for the top)