Line a cookie sheet with parchment paper and set to the side.
In a medium bowl add the butter and melt. Add sugar, brown sugar, and vanilla extract and mix until well combined. Crack the large egg in a small bowl and whisk until all combined and then measure out one tablespoon and add to the wet ingredients.
Mix the dry ingredients (flour, baking soda, salt) and mix until it begins to form a dough. Add in the chocolate chips and m&m.
Divide and roll the cookie dough balls. Decorate the top of the cookies with extra m&m and chocolate chips and then
Bake the cookies on the prepared baking sheet for 8 to 10 minutes. The m&m cookies will look golden brown with crisp edges. Allow the cookies to cool on the baking pan for 5 to 10 minutes before enjoying.
If there are leftovers store them in an airtight container for up to 3 days.