Line your 8x8 inch dish with parchment paper, leaving overhang on the sides for easy removal.
Gently melt the butter in a saucepan over low heat, stirring occasionally until it’s just melted and smells rich and buttery, about 2 minutes.
Add the chopped dark chocolate to the melted butter and stir continuously over low heat until the mixture is smooth, glossy, and fully melted, about 3 minutes.
Remove the saucepan from heat and stir in the sweetened condensed milk until the mixture is velvety and well combined, about 1 minute. It will become thick and glossy.
Stir in the vanilla extract and a pinch of sea salt, blending well to enhance the chocolate flavor and add a savory contrast.
Pour the fudgy mixture into your prepared dish, spreading it evenly with a spatula and pressing gently to smooth the surface.
If desired, sprinkle a tiny pinch of sea salt or chopped nuts on top for extra flavor and texture, pressing lightly into the surface.
Place the dish in the refrigerator uncovered and chill for at least 2 hours, or until the fudge is firm to the touch and has a shiny, crackly surface.
Once set, lift the fudge block out of the dish using the parchment overhang and transfer to a cutting board.
Use a sharp knife warmed in hot water to slice the fudge into even bars or squares, wiping the knife dry between cuts for clean edges.
Serve immediately or store in an airtight container in the refrigerator for up to a week. Enjoy these rich, creamy fudge bars straight from the fridge or at room temperature for a softer bite.
