Melt the butter in a large pan over medium-low heat. Once melted, add the marshmallows. Stir the mixture until the marshmallows are completely melted. Stir in the peanut butter and vanilla.

Remove from heat, then immediately fold in the cereal. Make sure each piece of cereal is coated with the peanut butter/marshmallow mixture.

Transfer mixture to 9 by 13-inch baking pan that has been lined with parchment paper and sprayed with nonstick spray. Gently press the mixture into the pan (lightly spray your hands with non-stick cooking spray to avoid the mixture sticking to your hands). Don’t pack it in too hard.

Put the chocolate chips in a medium-sized heatproof bowl. Microwave for 30-second intervals, stirring in between each interval. When they are almost melted, remove and stir until smooth. Pour the melted chocolate over the mixture and let cool to harden.

Allow treats to set for about an hour at room temperature. Lift the Rice Krispie Treats out of the pan using the parchment paper. Cut into squares.

Cover and store leftover treats at room temperature for up to 3 days. To store, place in layers between sheets of parchment or wax paper.