Using a 2-1/2-inch muffin pan, line eight muffin cups with paper bake cups; set pan aside.
In a small saucepan heat semisweet chocolate pieces and milk chocolate pieces over low heat, stirring constantly, until melted and smooth.
Remove saucepan from heat. In another small saucepan heat the peanut butter over low heat, stirring constantly, until melted. Remove saucepan from heat.
Pour about 1 tablespoon melted chocolate into each paper bake cup; chill about 5 minutes or until chocolate is firm. Pour about 1 tablespoon melted peanut butter over the firm chocolate in each paper bake cup; chill about 5 minutes more or until peanut butter is firm.
Pour the remaining melted chocolate evenly over the peanut butter layer in each paper bake cup, spreading the chocolate to cover the peanut butter. (If chocolate has stiffened a bit, return to low heat and stir until softened.) Sprinkle each with chopped peanuts.
Chill candy about 10 minutes more or until firm. Store tightly covered in the refrigerator. To serve, allow cups to stand at room temperature for 5 minutes.