Step 1: Prepare Your Pan - Grease your 9x13 inch baking pan with butter or cooking spray.
Step 2: Melt the Marshmallow Mixture - In a medium saucepan over low heat, melt 5 tablespoons of butter and add 4 cups of mini marshmallows. Stir until melted and smooth.
Step 3: Combine with Rice Cereal - Remove from heat and add 6 cups of crispy rice cereal, stirring until coated.
Step 4: Press into the Pan - Transfer the mixture into the baking pan and press evenly without packing too tightly.
Step 5: Make the Caramel Sauce - In a new saucepan, combine 1/2 cup of butter, 1/2 cup of light brown sugar, 1/2 cup of light corn syrup, and a dash of salt. Stir over medium heat until it boils, then boil for 2-3 minutes.
Step 6: Add Sweetened Condensed Milk - Remove from heat and stir in half of the condensed milk until fully incorporated.
Step 7: Pour Caramel Over Cereal Base - Pour the caramel sauce over the Rice Krispie mixture and spread evenly.
Step 8: Melt the Chocolate - In a microwave-safe bowl, combine chocolate chips and 1 tablespoon of butter. Microwave in intervals until melted and smooth.
Step 9: Drizzle the Chocolate - Pour melted chocolate over the caramel layer and spread evenly.
Step 10: Cool and Set - Cool at room temperature for at least 1 hour or refrigerate for quicker setting.