In the bowl of a stand mixer fitted with a paddle attachment, or using a hand mixer, cream together the butter and sugar on medium speed until light and fluffy, about 5 minutes.

In a small bowl, whisk together the flour, salt, baking soda, and baking powder.

Add the peanut butter into the butter and sugar mixture and beat until combined. Then mix in the egg and vanilla. Scrape down the sides of the bowl and give it one last stir to make sure everything is incorporated.

Dump in all of the flour mixture into the stand mixer bowl and beat on medium-low speed just until the last streaks of flour disappear.

Chill the dough for about an hour, or until it has firmed up a bit.

Portion out 14-15 dough balls on a half-sheet tray lined with parchment or a silicone mat. I find it’s easiest to do this with a 1.3-ounce cookie scoop or press-disher, or 2 tablespoons.

Using a piping bag or a spoon, top each dough ball with a dollop of marshmallow fluff, about 1 tablespoon each.

Chill the dough balls in the freezer for about 30 minutes.

Preheat the oven to 350°F. Place the oven racks in the top and lower thirds of the oven.

Place half the dough balls on another lined half-sheet tray.

Bake the cookies for 8 minutes, then rotate the trays and swap their rack placements to promote even baking. Giving them a firm *thwap* against the counter at this stage deflates them and gives them a crisp outside and chewy middle.

Bake for 8-9 more minutes. Remove the trays from the oven and let the cookies set up for about 5-10 minutes before transferring them to a wire rack to cool completely.