Preheat the oven to 350˚F. Line a baking sheet with parchment paper and set aside.
In a large bowl, cream together the butter and sugars until light and fluffy. Mix in the egg and vanilla until fully incorporated.
In a separate bowl, mix together the flour and baking soda. Slowly mix the flour mixture into the wet ingredients until fully combined. Fold in the M&Ms.
Using a cookie scoop, scoop the cookie dough onto the prepared baking sheet and bake in the preheated oven for 9-11 minutes, or until set on top. Remove from the oven and allow to cool completely on the baking sheet.