Grease a 9x9-inch baking pan. Line with parchment paper, allowing edges to extend over pan. Grease paper.Advertisement
Place chocolate and peanut butter in a large heatproof bowl. Set bowl over a pan of simmering water. (Water should not touch bottom of bowl.) Stir occasionally until melted and smooth. Stir in sweetened condensed milk, vanilla, and kosher salt until combined. Remove from heat.
Stir in marshmallows and peanuts. Transfer to prepared pan. Cover with plastic wrap; flatten mixture evenly. Remove plastic wrap. Sprinkle with sea salt and sugar.
Chill, covered, 2 hours or until firm. Cut into 1-inch pieces. Store in an airtight container in the refrigerator up to 1 month or freeze up to 2 months. Makes 81 pieces.
Layer fudge between waxed paper in an airtight container. Store in refrigerator up to 1 week or freeze up to 2 months.