Toast the Coconut: In a large sauté pan, add the entire bag of shredded coconut. Cook over medium-high heat, stirring constantly until it becomes mostly golden brown, about 5-7 minutes. Remove from heat and stir for an additional 2 minutes.

Prepare the Dulce de Leche Mixture: Set aside ½ cup of the toasted coconut for later. In a microwave-safe bowl, combine the dulce de leche with the milk. Microwave for 1 ½ minutes to soften and thin out the mixture, then stir well.

Mix with Coconut: Combine the dulce de leche mixture with the remaining toasted coconut, ensuring it's well-mixed.

Melt Marshmallows and Butter: In a separate large microwave-safe bowl, melt the mini marshmallows and butter together, about 2 minutes in the microwave. Stir to combine until smooth.

Combine with Cereal: Add the Rice Krispies cereal to the melted marshmallow mixture. Stir until evenly coated.

Layer the Mixture: Grease an 8×12-inch baking pan. Press half of the cereal mixture into the bottom, then spread the caramel-coconut mixture on top, followed by the remaining cereal mixture. Press down evenly.

Top with Chocolate: Melt the semisweet chocolate in the microwave and pour it over the top of the cereal bars. Sprinkle the reserved toasted coconut over the melted chocolate before it hardens.

Chill and Serve: Let the bars cool completely so the chocolate hardens. Once set, cut into squares and enjoy!