In a large bowl, combine the melted butter and sugars. Whisk to combine.
10 tablespoons unsalted butter, ½ cup granulated sugar, ½ cup brown sugar
Add the egg and vanilla extract and whisk until well combined.
1 large egg, 1 teaspoon pure vanilla extract
Add the flour, baking soda, and salt and stir just until no large lumps of flour remain.
1½ cups all-purpose flour, 1 teaspoon baking soda, ½ teaspoon kosher salt
Fold in the M&Ms until they’re combined-- you don’t want to overmix!
1 cup Halloween M&M's candies
Cover the bowl and transfer the cookie dough to the refrigerator to chill for 30 minutes.
While the cookie dough chills, preheat your oven to 350°F and line 2 baking sheets with parchment paper.
Once the dough has chilled, scoop 2-tablespoon-sized cookies onto the baking sheets, making sure they’re at least 2 inches apart.
Bake the cookies for 12-14 minutes, or until the edges are golden brown. Allow them to cool fully before removing them from the tray-- they will set as they cool.