Preheat oven to 350 degrees.
Grease a 12 inch round baking dish well, with butter. Set aside.
In a stand mixer with the paddle attachment, beat butter, granulated sugar, and brown sugar until light and fluffy.
Drop in eggs, one at a time, beating well after each addition.
Add pure vanilla extract and peanut butter. Beat until combined.
Beat in flour until combined.
Press dough into the prepared baking dish, spreading evenly.
Bake for 20 minutes or until the edges are starting to turn lightly brown.
Take cookie out of the oven, sprinkle mini-marshmallows and chocolate chips over the top. Bake for an additional 3 mintues.
Remove from oven, sprinkle Holiday M&M's over the top and cook for an additional 2 minutes.
Let cool for 10-15 minutes. Cut into slices, serve and enjoy!
If serving later, warm in the microwave for a 1-2 minutes to soften the marshmallows.