Preheat your oven to 350°F (175°C) and grease two 9-inch round cake pans. In a large mixing bowl, cream together butter and brown sugar until light and fluffy. Add eggs one at a time, mixing well after each addition. Melt the dark chocolate and stir it in along with the cocoa powder, blending until fully incorporated.

In a separate bowl, sift together flour and sea salt. Gradually fold this dry mixture into the wet ingredients until just combined.

Pour the chocolate batter evenly into the prepared cake pans. Bake in the preheated oven for 30-35 minutes, or until a toothpick inserted comes out clean.

While the cake cools, prepare the caramel. In a saucepan over medium heat, add sugar and allow it to melt without stirring. Whisk in heavy cream and remove from heat to cool slightly until thick.

Once the cakes are completely cool, place one layer on a serving plate. Drizzle with caramel and repeat with the second layer.

Slice the cake into pieces, drizzle additional caramel over each slice before serving, and garnish with a sprinkle of sea salt.