Preheat the oven to 450 degrees F (232 C). Yes, I know it's a lot hotter than your average cookie baking temperature. Line a couple baking sheets with parchment paper. In a large bowl, whisk the GF flour, cornstarch, salt, and baking soda together.
Cream the butter, peanut butter, sugar, and molasses together using a stand mixer. while it's mixing, pour in the vanilla and mix until fluffy and well combined. Add both eggs and beat until fully mixed. Scrape the sides and bottom of the bowl with a spatula. Add the dry mixture and rolled oats and mix on low until combined then turn the speed up to high and let it mix a little longer. Add the chocolate chips and M&M's and mix until they are just combined, over mixing will crush the M&M's.
Scoop the dough into large cookie dough balls, mine were the size of 2 heaped standard cookie scoop balls combined into one large ball. Each dough ball weighed about 85 grams or roughly 3 oz. Place 6 cookies spaced out evenly on one tray. Bake one tray at a time for 6 minutes. The top should be very lightly browned and the center should be very soft. Let them cool for at least 5 minutes before enjoying warm. If the cookies cool down, microwave for 10-15 seconds to make them soft and melty again before eating. Enjoy!
