Preheat oven to 400°F
Line a square baking pan (9 inch X 9 Inch) with parchment paper
Combine melted butter with cookie crumbs in a bowl. Transfer the crumb mixture to the prepared baking pan. Press evenly onto the bottom. Bake for 10 minutes.
Combine melted peanut butter with Rice Krispie in a bowl. Pour the mixture into the baked crust. Use a spatula to make it even.
Put the chocolate bar on top and bake for 3 minutes.
Now add the mini marshmallows and broil for 2 minutes.
Let it cool down and refrigerate for couple hours before cutting into individual pieces.