Preheat the oven to 350ºF. Line a baking sheet with parchment paper.

In a large bowl, or the bowl of a stand mixer, cream the butter and both sugars until light and fluffy. Add in both of the eggs, one at a time, scraping down the sides of the bowl in between additions. Beat in the vanilla.

In another bowl, combine the flour, baking soda, salt and pudding mix. Add the dry ingredients to the mixing bowl and mix just until combined. Stir in the peanut butter chips and the marshmallows.

Using a medium cookie scoop, drop the dough on the cookie sheet at least 2 inches apart. Bake until the cookies are just set, about 10 minutes. Let the cookies cool for 10 minutes on the baking sheet before transferring to a wire rack to cool completely. Repeat with the remaining dough.