Use softened butter to lightly butter the bottom and sides of an 8x8-inch pan. Set aside.
On the stove top in a heavy bottomed large saucepan or pot, melt together the sweetened condensed milk and peanut butter. Cook over medium-low for around 8-10 minutes until heated through and bubbling gently. Stir constantly to avoid sticking.
Remove from the heat adding the vanilla extract and the peanut butter chips. Stir until the chips are completely melted.
Mix-in the chopped Nutter Butter cookies and marshmallows. Stir until evenly distributed. Some marshmallows should remain whole.
Working quickly spread into the prepared pan. Sprinkle the top with chopped peanuts.
Chill 2 hours or until set, then cut into desired sized pieces. Store chilled in an airtight container.
Notes
Peanut Butter: You can experiment using other nut butters in place of peanut butter.
Baking Chips: You can use semi-sweet chocolate chips, butterscotch chips or white chocolate chips in place of peanut butter chips to change the flavor profile.
Cookies: You can use a different sandwich cookie to complement the flavor that you want to create.