Preheat your oven to 350°F (175°C). Line a 9x13 inch baking pan with parchment paper, allowing some overhang for easy removal later.

In a medium saucepan over low heat, combine the melted butter and granulated sugar. Stir until the sugar is dissolved and the mixture is smooth.

Remove from heat and add the melted semi-sweet chocolate chips. Stir until fully combined.

In a mixing bowl, pour the chocolate mixture over the crispy rice cereal. Gently fold the cereal into the chocolate until evenly coated.

Spread the mixture evenly into the prepared baking pan, pressing it down firmly with a rubber spatula to create an even layer.

Bake in the preheated oven for 10-12 minutes until set. Remove from oven and let cool completely.

In a small saucepan, combine the caramel sauce and heavy cream over low heat. Stir until smooth and well combined.

Once the base is cooled, pour the caramel mixture over the chocolate rice cereal base, spreading it evenly with a spatula.

Let the caramel layer set at room temperature for about 10 minutes.

In a double boiler or microwave-safe bowl, melt the milk chocolate chips until smooth, stirring frequently to avoid burning.

Once melted, pour the chocolate over the caramel layer, spreading it evenly.

If using, sprinkle the chopped nuts on top of the melted chocolate before it sets.

Allow the bars to cool at room temperature until the chocolate is set, about 30 minutes.

Once set, lift the bars out of the pan using the parchment paper overhang. Cut into 12 squares.

Store any leftovers in an airtight container at room temperature for up to 5 days.