Prepare a muffin tin with 6 liners (or you can use a chocolate mold).
Melt chocolate chips, in a microwave safe bowl, at 30-second intervals until melted, stirring in between.
Drop a tablespoon of melted chocolate into each muffin liner and drag the chocolate up the sides of the liner with a spoon. Place in the fridge to set.
Meanwhile, mix together the peanut butter and powdered sugar in a small bowl.
Scoop 2 teaspoons of the peanut butter mixture into each chocolate shell and press down to fill. Refrigerate for 5 minutes.
Top peanut butter cups with the remaining melted chocolate. Tap the muffin tin to level out the chocolate. Place back in the fridge and allow to fully set, about an hour.
Notes
Melt chocolate in the microwave using short intervals. Or use a gentle double boiler instead.
Add a bit extra confectioner sugar to firm up the nut butter.
Refrigerate homemade peanut butter cups for up to two weeks, or up to three months in the freezer. Serve at room temperature.