Chocolate Peanut Butter-Cup Treats

Line a 13x9-inch baking pan with nonstick foil, extending foil 2 inches beyond the edges. In a 6-quart pot, melt butter over medium-low heat. Add marshmallows and stir with a rubber spatula until almost melted. Add peanut butter and vanilla to marshmallow mixture and stir until smooth. Remove from heat. Stir in cereal until it’s evenly coated with the marshmallow mixture. Press mixture into pan in an even layer and cool completely. Melt chocolate chips in microwave, then drizzle over cooled cereal. Scatter peanut butter cup pieces on top and refrigerate until chocolate hardens. Remove from pan and peel off foil. Cut into 24 squares. Store in an airtight container.