Line a standard 12-cup muffin pan with 12 paper liners and set aside.

Place the 12 ounces milk chocolate chips in a medium microwave-safe bowl. Microwave on high for 1 minute, stir, then continue heating in 30-second intervals, stirring after each interval, until the chocolate is completely melted and smooth. Keep the melted chocolate warm and pourable; if it begins to firm before assembly you can reheat it briefly (see step 9).

Using about 1 teaspoon of the melted chocolate per cup, spoon the chocolate into the bottom of each liner and gently spread it to cover the bottom (and a little up the sides, if you like) to form a chocolate base. Put the pan in the refrigerator to set while you prepare the fillings.

In a small microwave-safe bowl combine the 1 cup caramel bits and 2 tablespoons water. Microwave on high for 1 minute, stir, then heat in 20-second intervals, stirring after each, until the caramel is fully melted and smooth. Be careful — the mixture will be hot.

Stir the ½ cup rough chopped peanuts into the melted caramel until evenly combined. Set the caramel-peanut mixture aside to cool slightly so it is scoopable but still pourable.

In a small mixing bowl combine the ⅔ cup creamy peanut butter and the ⅓ cup powdered sugar. Stir thoroughly until smooth and evenly mixed. The mixture should be thick but scoopable.

Remove the muffin pan from the refrigerator once the chocolate bases are firm to the touch.

For each chocolate cup, scoop about 2 teaspoons of the peanut butter mixture into the center and gently spread it, leaving space around the edges for the chocolate top.

Spoon about 1 tablespoon of the caramel-peanut mixture over the peanut butter layer in each cup, spreading gently to cover the peanut butter.

Top each cup with about 2 teaspoons of melted chocolate to seal. If the reserved melted chocolate has hardened, reheat it in the microwave in 10–15 second bursts, stirring between bursts, until smooth and pourable before topping.

Return the pan to the refrigerator and chill the cups until the chocolate is fully firm, about 20–30 minutes. Remove from the liners to serve.