Line your 9x9 inch pan with parchment paper, leaving some overhang for easy lifting later.
Place the chopped dark chocolate in a heatproof bowl.
Set up a saucepan with simmering water and place the bowl over it, creating a double boiler.
Gently stir the chocolate until it melts completely and becomes glossy, about 5-7 minutes. You’ll notice the aroma of cocoa filling your kitchen.
Add the small cubes of butter to the melted chocolate and stir until fully incorporated and smooth.
Stir in the sweetened condensed milk and vanilla extract, blending until the mixture thickens into a velvety, uniform batter.
Pour the chocolate mixture into your prepared pan, using a spatula to spread it evenly across the surface.
Gently tap the pan on the counter to level the mixture and release any air bubbles. Sprinkle a pinch of sea salt over the top for a savory contrast.
Place the pan in the fridge and chill for at least 2 hours, or until the mixture is firm, shiny, and crackly on top.
Once set, lift the slab out of the pan using the parchment overhang and transfer onto a cutting board.
Use a sharp knife to cut into bars or squares, wiping the blade between cuts for clean edges. Serve immediately or store in an airtight container in the fridge.
