In large saucepan melt butter over low heat. Add 4 cups marshmallows and stir until completely melted. Remove from heat. Stir in peanut butter until melted.
Stir in Rice Krispies and remaining 2 cups of mini marshmallows until well coated. Press into a greased 9x13 pan and set aside.
Place caramels and heavy cream into a small bowl. Microwave in 20-30 second intervals until completely melted. Pour overtop Krispie treats and spread until mostly covered. Sprinkle with sea salt and cool.
Cut into bars using a sharp knife and serve. Store in airtight container for up to 5 days.