Line a mini muffin tin with mini liners, and set the pan aside.
In a medium microwave-safe bowl, heat half of the chocolate, starting with 1 minute, and then checking and stirring every 30 seconds, until it is completely melted and smooth.
24 ounces melting chocolate
Spoon about 1 teaspoon of the melted chocolate into the bottom of each mini liner, until the chocolate is completely used. Let that layer of chocolate cool and set while you prepare the peanut butter filling.
In a medium saucepan, heat the peanut butter and butter together until they are melted. Remove from heat and then stir in the powdered sugar and vanilla until it thickens.
1 cup creamy peanut butter, ¼ cup unsalted butter, 1½ cups powdered sugar, 1 teaspoon pure vanilla extract
Drop about 1 teaspoon of the peanut butter mixture onto the cooled chocolate in the liners. Repeat until all of the cups have been topped with some of the peanut butter.
Melt the remaining half of the chocolate, and then drop about 1-1½ teaspoons over the peanut butter mixture, covering the entire top. Once they have all been covered, tap the pan onto the counter until the tops are smooth.
Let the cups sit until they are cooled, for about 30 minutes.