Melt butter in a large pot. Add mini marshmallows and stir constantly until melted. Remove from heat and add vanilla and a pinch of salt. Then add rice krispie cereal and stir gently until cereal is coated.
Scrape the mixture into greased baking dish and press down in an even layer. Place dish in the refrigerator to cool for about 30 minutes. Then cut into squares.
Melt chocolate: place chopped dark chocolate in a microwave save bowl and microwave on high in 1-minute intervals until melted. Then stir in corn syrup.
Place dipped treats on a cooling rack. Place the cooling rack in the refrigerator for 20 minutes to set the chocolate. Once cooled, sprinkle with sea salt, if desired. Enjoy!