Halloween Monster Cookies

Preheat the oven to 350° F (177℃). Prepare baking sheet pans with silicone baking mats or parchment paper.
In the bowl of a stand mixer fitted with a paddle attachment or in a large mixing bowl with an electric hand mixer, cream the unsalted butter, light brown sugar, and granulated sugar until smooth and creamy. Add in the peanut butter and mix until smooth. Add the eggs and vanilla extract and mix until well combined.
Add in the all-purpose flour, quick oats, baking soda, and salt and mix on low speed until the cookie dough forms. Fold in the semisweet chocolate chips and M&M candies until they are well dispersed throughout the cookie dough.
Portion the cookie dough using a large cookie scoop (3 tablespoons). Place the cookie dough balls on the prepared baking sheet pans allowing room for spreading. Press additional chocolate chips and Halloween M&Ms into the cookie dough balls, if desired.
Bake the cookies for 11 to 12 minutes until set on the edges. Cool the cookies on the pan for 2 minutes and then transfer to a wire rack to cool completely .