Cream the unsalted butter, light brown sugar, and granulated sugar until light and fluffy, about 1 minute.
12 tablespoon unsalted butter, ½ cup granulated sugar, ⅔ cup light brown sugar
Mix in the egg, egg yolk, and vanilla extract until completely combined, scraping down the bowl as necessary.
1 large whole egg, 1 large egg yolk, 2 teaspoon vanilla extract
Fold in the flour, salt, and baking soda until almost combined, then add the mini m&m's and mini chocolate chips. Fold until just combined and there are no more dry flour pockets.
1 ¾ cup all-purpose flour, ½ teaspoon salt, 1 teaspoon baking soda, ⅓ cup mini m&ms, ¾ cup mini semi sweet chocolate chips
Scoop the dough with a large cookie scoop, about 3 tablespoons of dough, and place them on a lined baking tray.
Chill the dough in the freezer for 15-20 minutes, or until completely solid. Or chill them in the fridge for 45-50 minutes.
Preheat the oven to 350 F/180 C.
Bake the cookies spaced 2-3 inches apart for 12-15 minutes, or until the edges are just golden brown and the middle is puffy.
As soon as they come out of the oven, carefully press more m&m's and chocolate chips onto the tops of each. Let them cool completely on a wire cooling rack then enjoy!