Preheat oven to 350°F (175°C) and grease a 9x13-inch baking dish.
Crush Nutter Butter cookies into fine crumbs and mix with melted butter. Press into the prepared baking dish to form the crust.
Pour the sweetened condensed milk evenly over the crust.
Sprinkle chocolate chips, mini marshmallows, and nuts (if using) over the milk layer.
Bake for 20-25 minutes or until the marshmallows are golden brown and the edges are bubbly.
Cool completely before cutting into bars and serving.