Line a standard 12-cup muffin tin with liners. Set aside.
In a medium bowl, combine the peanut butter, butter, and confectioners' sugar. Using a hand mixer on low speed, blend everything together until smooth and well mixed. Set aside.
Place the chocolate in a microwave safe bowl. Heat in 20 second intervals, stirring after each one, until the chocolate is fully melted and smooth, about 1 to 2 minutes total.
Spoon about 1 tablespoon of chocolate into the bottom of each muffin cup, just enough to cover the base of the liner. Place 2 heaping teaspoons of the peanut butter mixture in the center. Add another tablespoon of chocolate on top of each one. Gently tap the muffin tin on the counter to help the chocolate spread evenly and smooth the tops.
Chill in the refrigerator for 1 hour, or until set, before serving.
