Preheat the oven to 350℉. Line a baking sheet with parchment paper or silicone baking mat. Set aside.
Cream together peanut butter, butter, brown sugar and granulated sugar in a stand mixer on medium speed until light and fluffy. Scrape down the sides of the bowl, as needed.
Mix in the egg and vanilla extract until combined.
In a medium bowl, combine the flour, baking soda, and salt. Mix the dry ingredients into the wet ingredients on low speed until incorporated, scraping the sides as needed.
Measure 2 tablespoons of dough and roll into a smooth bowl. Place the balls 2-3 inches apart on the baking sheet. Using your hands, flatten each ball into a roughly 3-inch flat disk.
Using a spoon or piping bag, fill the centers of the disks with ½ to 1 tablespoon of marshmallow fluff/creme. Carefully fold the dough over the top of the marshmallow creme, completely covering it and forming a ball. *If you find the dough a little sticky, refrigerate for 20-30 minutes then try again. Results tend to vary based on the type of peanut butter you used.
Bake the cookies 10-12 minutes, or until lightly golden around the edges. Watch the cookies as they near the 10 minute mark to ensure you don't overcook them and that the marshmallow doesn't burn. You'll want these to be slightly underbaked in the center for nice soft cookies once they cool and set.
Press the peanut butter chips into the cookies while they are still hot. Allow the cookies to cool for 10-15 minutes on the cookie sheet before serving.