These are addictive. I got this recipe from The Washington Post.
1 ½ T butter
1 C natural creamy peanut butter*
1 14 oz can sweetened condensed milk
2 C mini marshmallows
16 oz unsalted roasted peanuts
Line a 9" square baking dish with plastic wrap, leaving enough overhang to use as handles to remove the candy slab later.
Combine butter and peanut butter in large saucepan over medium heat, stirring until smooth. Stir in sweetened condensed milk and marshmallows; cook for about 3 minutes, stirring, or until smooth. Remove from heat.
Stir in the peanuts until evenly distributed. Working quickly, pour into prepared dish, smoothing it into the corners. Let cool 30 minutes, then freeze 30 minutes to firm.
Use the plastic wrap handles to lift the slab out of the pan and onto a cutting board. Cut into 24 equal pieces and serve, or store in the refigerator between layers of parchment or wax paper for up to 2 weeks.
*Use natural peanut butter here. Regular PB, with added shortening, will make the bars too greasy.