Prep your pan. Grease a 9×13-inch baking dish with butter or nonstick spray. You can also line it with parchment paper for easy removal.

Melt the butter and marshmallows. In a large pot over medium heat, melt the butter. Once melted, add the bag of mini marshmallows (reserve 1 cup for later) and stir until fully melted and smooth.

Add the pudding mix. Remove from heat and immediately stir in the dry banana pudding mix and vanilla extract, if using. The heat will help dissolve the mix and distribute the flavor evenly.

Mix in the cereal and wafers. Quickly fold in the Rice Krispies cereal and chopped vanilla wafers. Stir until everything is evenly coated. Then fold in the reserved 1 cup of mini marshmallows for gooey pockets of marshmallow throughout.

Press into the pan. Transfer the mixture to your prepared pan. Gently press it down with a spatula or greased hands to spread it out evenly. Don’t pack too tightly, or the bars can become hard.

Cool and slice. Allow to cool completely at room temperature for at least 30 minutes before slicing into squares or bars. Store in an airtight container once cooled.