Adjust your oven rack to the second level mark (just above center), preheat your oven to 350ºF, and line 2 baking sheets with parchment paper. Set them to the side.

Whisk together the all-purpose flour, baking soda, and salt in a small bowl. Set aside.

In a mixing bowl, beat together the peanut butter and unsalted butter until creamy.

Add the granulated sugar and light brown sugar, mixing until well blended.

Add the egg and vanilla extract, mixing until fully combined.

Gradually add the dry ingredients to the wet mixture, mixing until just combined.

Using a 2-tablespoon size cookie scoop, scoop out a ball of cookie dough and place it onto the baking sheet.

Press the ball down into a round disc shape that’s roughly 3 inches in diameter.

Scoop a small ball of marshmallow fluff into the center of your cookie disc.

Fold the cookie dough over the marshmallow fluff and shape it back into a ball.

Roll the ball in granulated sugar and place it back onto the baking sheet.

Repeat until all cookie dough balls have been formed.

Bake the cookies for 10-12 minutes until golden around the edges.

Let the cookies cool on the baking sheet for 5-10 minutes before transferring to a cooling rack.