- 4 tabelspoons (1/2 stick) unsalted butter, plus more for the pan
- 1 10-ounce bag large marshmallows (about 6 cupes)
- 3/4 teaspoon fine salt
- 1/3 cup plus 1 tablespoon creamy peanut butter
- 6 cups rice cereal (such as Rice Krispies)
- 3 ounces semisweet chocolate, chopped
- 1 1/4 cup (about 20) miniature chocolate peanut butter cups, chopped
- Butter an 8-inch square baking pan. Line with 2 crisscrossed pieces of parchment, buttering in between and leaving and overhand on all sides; butter the parchment.
- Melt the butter, marshmallows, salt, and 1/3 cup of the peanut butter in a medium pot over medium heat. Remove from the heat and stir in a rice cereal. Press into the prepared pan.
- Place the chocolate and the remaining tablespoon peanut butter in a large microwave-safe bowl. Microwave on high in 30-second intervals, stirring in between, until melted. Spread on the bars. Sprinkle with the peanut butter cups. Let sit until the chocolate is set, 1 to 2 hours.
- Holding the paper overhang, lift the bars out of the pan and transfer to a cutting board. Cut into 16 squares (4 rows by 4 rows).