Melt the butter in a pot on the stove over medium heat.
Add marshmallows, peanut butter, and vanilla extract, stirring until everything melts together.
Once smooth, remove from heat and stir in the Rice Krispie cereal until fully combined.
Transfer the mixture to a greased 8×8 baking dish and press it down evenly with a spatula.
Melt the chocolate chips and coconut oil together, then pour over the rice crispy treats.
Sprinkle crushed peanuts on top if desired.
Refrigerate for two hours until solid, then slice into squares and enjoy the nostalgia! Store any leftovers in the fridge for up to one week.