Melt butter in a large stock pot over medium heat. When melted, add all but 1 c marshmallows and stir frequently.
Add in sweetened condensed milk and nutella, and stir together until combined.
Remove from heat and pour in cereal, toss to coat. Now toss in remaining 1 c marshmallows and toss to combine.
Spread onto a large piece of wax paper and shape into a rectangle. Let cool completely before cutting into heart shapes.
Add chocolate to a bowl with 1 tsp coconut oil, and melt in 30 second intervals until melted. Drizzle on top and garnish with Maldon sea salt and sprinkles.