Line a standard 12-cup mini muffin tin with paper liners.
Melt half a bag of milk chocolate chips in the microwave for 30 seconds; stir; cook in 10-second increments, stirring after, until melted. Be careful not to scorch the chocolate.
With a small spoon or cookie scoop, evenly distribute melted chocolate into each muffin cup. Drop the pan repeatedly on the counter to help chocolate flatten and smooth out. Freeze the whole pan for 10 minutes.
In a separate bowl combine peanut butter, powdered sugar, and butter. Beat with an electric hand mixer until smooth and creamy.
Remove the pan from the freezer and place small spoonfuls of the peanut butter mixture on top of each chocolate layer. Drop pan repeatedly on the counter again, to help flatten the peanut butter layer. Freeze the whole pan for 10 minutes.
Melt the remaining half bag of milk chocolate chips. Working quickly, portion small spoonfuls of chocolate into each cup, three cups at a time, immediately dropping the pan repeatedly on the counter to flatten cups. Side Note: Do this every three cups because the frozen peanut butter layer will harden the melted chocolate very quickly.
Freeze the whole pan for 10 minutes to set the top layer of chocolate. Store in the refrigerator in an airtight container. Enjoy.