Line an 8x8-inch baking pan with parchment paper, leaving an overhang on the sides for easy removal, and lightly grease it with non-stick cooking spray.

In a large pot over low heat, melt 1/2 cup of unsalted butter, then add 10 ounces of mini marshmallows, stirring constantly until completely melted and smooth.

Remove the pot from the heat, then gently stir in 1/2 cup of caramel sauce and 1/2 teaspoon of coarse sea salt until the mixture is fully combined.

Add 5 cups of puffed rice cereal to the warm marshmallow mixture, folding gently with a greased spatula until every piece of cereal is evenly coated.

Transfer the mixture into the prepared baking pan, using a piece of wax paper or a greased spatula to press it down gently into an even layer without packing it too tightly.

In a microwave-safe bowl, combine 1.5 cups of semi-sweet chocolate chips and 1 tablespoon of butter, heating in 30-second intervals and stirring until completely smooth and melted.

Pour the melted chocolate over the crispy treats, spreading it evenly to the edges, then sprinkle a pinch of extra sea salt on top before letting it cool in the refrigerator for 30 minutes to set before slicing.