Preheat oven to 350 degrees F. Line a baking sheet with parchment.
In a medium bowl, stir together peanut butter, sugar, baking soda, and egg until well combined.
Take roughly golf ball sized pieces of the dough and spread out into a disc using your hands. Place a heaping tablespoon of fluff in the center and wrap the dough around it, covering it as much as possible. They will ooze some, especially during baking, but don’t worry.
Once all the cookies are finished, bake for about 12 minutes until just barely golden brown and starting to set. Serve warm or cool completely on the pan. Cookies may be stored in an airtight container at room temperature for up to 5 days or frozen wrapped in parchment and foil and placed in a zipper bag for up to 3 months. Thaw at room temperature for about an hour or in the microwave for about 30 seconds.