Melt the dark chocolate using a double boiler or microwave in short bursts, stirring until smooth, then let cool slightly.

In a large bowl, beat the butter, brown sugar, and white sugar until fluffy. Add the eggs one at a time, followed by the vanilla extract.

Gradually add the dry ingredients (flour and cocoa powder) to the wet mixture, mixing just until combined.

Gently fold in the melted chocolate until the dough is rich and glossy.

Scoop the dough, insert a small piece of chocolate or caramel into the center of each portion, and roll into balls. Freeze the dough balls to help set the molten effect.

Preheat the oven to 350°F (175°C) and bake the frozen dough balls for 10-12 minutes, until the edges are set but the centers remain soft. Finish with a sprinkle of flaky sea salt.