Prepare caramel: Stir ingredients in a medium saucepan over medium-low heat until melted and smooth. Remove from heat. Line a 13x9-inch baking pan with nonstick foil, extending foil 2 inches beyond the edges. In a 6-quart pot, melt butter over medium-low heat. Add marshmallows and stir with a rubber spatula until almost melted. Stir in vanilla, 1 tsp of the sea salt, and 1 cup of the caramel mixture. Continue to stir until mixture is blended and smooth. Remove from heat. Stir in cereal until it’s evenly coated with the marshmallow mixture. Press mixture into pan in an even layer and cool completely. Spread the remaining 1 cup of the caramel mixture over cooled cereal. Sprinkle with the remaining 2 tsp of the sea salt. Remove from pan and peel off foil. Cut into 24 squares. Store in an airtight container.