In a large microwave-safe bowl, combine unwrapped caramels, sweetened condensed milk, and butter. Microwave in 1-minute increments, stirring until smooth and creamy, about 3-4 minutes. Set aside to cool slightly.

In a saucepan over low heat, melt 3 tablespoons of butter with 4 cups of miniature marshmallows. Stir continuously until smooth. Once melted, fold in 6 cups of Kellogg's Rice Krispies cereal.

Grease a 9 x 13-inch pan and press the warm Rice Krispie mixture into the bottom evenly. Allow to cool slightly.

Pour the caramel mixture over the pressed Rice Krispie layer, spreading it evenly. Optionally sprinkle mini marshmallows on top.

Melt another 3 tablespoons of butter with 4 cups of miniature marshmallows in a saucepan. Mix in 6 cups of Kellogg's Rice Krispies cereal until combined.

Press the second Rice Krispie mixture on top of the caramel layer, ensuring it's even. Let cool at room temperature for about 10 minutes.

Chill in the refrigerator for about 30 minutes to firm up before cutting into squares.