Evenly coat a 8x8 glass baking pan with coconut oil spray to prevent sticking.
In a medium-large pot, melt the butter over medium-low heat.
Stir in the marshmallows and continue to stir until melted. My mixture was still a little lumpy.
Remove from heat, then stir in the vanilla and salt.
Gently fold in the cereal until evenly coated.
Press the marshmallow cereal mixture into the greased pan.
Let the treats set for one hour before slicing.
Once cooled, wrap tightly with plastic wrap. Best if enjoyed within 3 days.
Optional peanut butter chocolate topping: Right before serving, spread a layer of peanut butter over the top of the bars, then drizzle with melted chocolate.