In a heavy-bottomed pot, melt 4 tablespoons of unsalted butter over low heat, stirring frequently to avoid browning. The butter should be just melted and glossy, taking about 2-3 minutes.

Once the butter is melted, add in 10 ounces of mini marshmallows. Stir the mixture constantly over low heat until the marshmallows are fully melted and smooth, which should take about 4-5 minutes.

Remove the pot from the heat and immediately whisk in 1 cup of banana pudding mix until well combined. The mix should blend smoothly with the marshmallow mixture.

Gently fold in 6 cups of Rice Krispies and the optional crushed vanilla wafers, using a spatula or wooden spoon.

Lightly grease a 9x9-inch baking pan with cooking spray or butter. Transfer the mixture into the pan and press it down evenly with a piece of wax paper or parchment.

Sprinkle additional crushed vanilla wafers on top and gently press them into the mixture for a decorative touch. Allow the treats to sit at room temperature for 30-45 minutes to set.

Once the mixture has set, use a sharp, greased knife to cut it into squares.