6 oz. good-quality dark chocolate, finely chopped
1-1/4 sticks unsalted butter, cut into small pieces
3 large eggs
1 cup superfine sugar
1/3 cup ground hazelnuts or almonds
1/4 cup good-quality cocoa powder
Pinch of salt
Preheat the oven to 350F. Place an oven rack in the lower third of the oven.
Microwave the chocolate and butter together in a large bowl until melted.
Using an handheld electric mixer, whisk the eggs and sugar to combine. Add the melted chocolate and mix gently to combine.
Grind the nuts, then fold in with the cocoa powder and salt.
Transfer to a 9-inch cast-iron skillet and bake for 25 minutes.