In a saucepan over low heat, melt the unsalted butter and peanut butter together, stirring until smooth.

Once melted, add the mini marshmallows and honey (if using) to the saucepan. Stir continuously until the marshmallows are completely melted and the mixture is smooth.

Remove the saucepan from heat and quickly add the Rice Krispies cereal to the mixture. Stir until all the cereal is evenly coated.

Transfer the mixture to a greased 9x9 inch baking dish. Press down firmly with a spatula to create an even layer.

Allow the treats to cool at room temperature for about 10 minutes before cutting into squares.