Grease an 11" x 7" pan to prevent the nut squares from sticking.

Evenly spread 1½ cups of salted peanuts on the bottom of the pan to create a crunchy base.

In a large saucepan, combine butter and peanut butter chips. Heat over low, stirring constantly until smooth, about 10 minutes.

Remove the saucepan from heat. Stir in sweetened condensed milk and marshmallows, mixing until fully melted and smooth.

Pour the peanut butter mixture over the peanut layer in the pan and spread evenly with a spatula.

Sprinkle the remaining 1½ cups of salted peanuts on top. Optionally, add a pinch of kosher or sea salt.

Cover the pan and refrigerate for at least 2 hours until set.

Once set, cut the bars into squares. Serve chilled for a firm texture, or allow to reach room temperature for a softer bite.