In the bowl of a stand mixer, cream together the peanut butter and butter until well blended. Add in the vanilla and mix again. Then add in the powdered sugar. Mix on low speed until all of the powdered sugar is mixed in.

Line a small cookie sheet with wax paper. Press the peanut butter mixture onto the wax paper, making a rectangle that is about 9"x7". The peanut butter will be about 1/4 to 1/2 inch thick.

Put the cookie sheet into the freezer for 10-15 minutes.

Once the peanut butter is firm, spread the marshmallow fluff on top, leaving 1/2 an inch of peanut butter showing on all sides of the rectangle. Allow the layers to sit for about 10 minutes to bring it closer to room temperature.

Fold the layers in half and press the edges together, to enclose the marshmallow inside the peanut butter. Then gently mold the mixture into a ball, being careful to keep the marshmallow fluff hidden inside.

Sprinkle the mini chocolate chips on the cookie sheet and roll the peanut butter ball in the chips, coating the outside.

Wrap the ball tightly in plastic wrap and refrigerate until serving.