Halloween Monster Cookies

Preheat oven to 350° F. Line baking sheet pans with silicone baking mats or parchment paper.
In a large mixing bowl or bowl of a stand mixer fitted with a paddle attachment, on medium speed cream unsalted butter, peanut butter, and brown sugar until smooth.
Add egg and vanilla extract and continue to mix until well combined.
Add baking soda, cornstarch and salt and mix on low until combined.
Add in quick oats and all-purpose flour. Mix on low speed until the wet and dry ingredients are well incorporated. Scrape the sides and bottom of the bowl to ensure the cookie dough is well mixed.
With a spatula or spoon, fold in semisweet chocolate chips and M&Ms until they are well dispersed throughout the batter.
Using a large cookie scoop (3 tbsp), portion the cookie dough and place onto the prepared baking trays allowing room in between the dough balls for spreading.
Bake for approximately 10-12 minutes until the cookies are set and slightly golden brown on the outside but appear underdone in the middle.
Remove from the oven and allow the cookies to cool for 2-3 minutes on the baking pan. Press additional M&Ms in the top of the cookies for extra color.
Transfer the cookies to a wire rack to cool completely.