Place the peeled and quartered potato in a small pot, cover with cold salted water, bring to a boil, and cook for 8–10 minutes until fork-tender.

Drain the potato in a colander and transfer it to a medium mixing bowl; mash thoroughly with a fork or whisk until completely smooth.

Let the mashed potato cool for 3–5 minutes until warm but not hot.

Stir in the softened butter and creamy peanut butter until the mixture is homogenous and creamy.

Add 2 cups of powdered sugar and mix well; continue adding sugar 1/2 cup at a time until a thick, fudge-like dough forms (you may not need the full 4 cups).

Line an 8×8-inch baking pan with parchment paper, pressing the mixture evenly into the pan to about 1/2-inch thickness.

Refrigerate for 30 minutes or until firm enough to cut cleanly.

Lift the chilled slab out of the pan using the parchment overhang and cut into 36 squares, roughly 1.5 inches each.

Melt the semi-sweet chocolate in a microwave-safe bowl in 30-second intervals, stirring between each, until smooth (about 1½ minutes total).

Using two forks, dip each candy square into the melted chocolate to coat, then place on a parchment-lined sheet.

Allow the chocolate to set at room temperature for 15 minutes or refrigerate for 10 minutes before serving or storing.