In a large bowl, whisk together the flour, baking soda, baking powder and salt. Stir in the oats.
In a medium bowl, whisk the melted butter and brown sugar together until smooth & combined. Whisk in the vanilla, peanut butter and then the egg until well incorporated. Pour the wet ingredients into the dry ingredients and gently mix together with a wooden spoon or spatula until just combined. Fold in the white chocolate chips and M&M's reserving 1/4 cup of each for topping if desired. Place dough in the fridge to chill for 30 minutes.
Once dough is chilled, preheat oven to 350 F degrees. Line two cookie sheets with parchment paper or silicone baking mats.
Using a large cookie scoop or measure and roll 2-1/2 tablespoon size cookie dough balls. Place about 8 balls onto prepared cookie sheet.
Bake in preheated oven for 10-12 minutes for a soft and underbaked cookie. they will continue to bake on the cookie sheet. Press a piece or two of the remaining chocolate chips and M&M's into each cookie if desired. Cool on the cookie sheet for 10 minutes before transferring to a wire rack.
Soft and Chewy Oatmeal Monster Cookies
Amount Per Serving (2 cookies)
Calories 293Calories from Fat 135
% Daily Value*
Total Fat 15g23%
Saturated Fat 7g35%
Total Carbohydrates 33g11%
Dietary Fiber 1g4%
* Percent Daily Values are based on a 2000 calorie diet.