Preheat the oven to 355°F (180°C) on convection mode.

Melt the dark chocolate and butter in a pot or in the microwave in short bursts. Stir in the eggs and whisk until combined. Add the white flour, sugar, and a pinch of salt, and mix until the batter is smooth and uniform.

Transfer the mixture to about 1/3 height in individual rings or baking dishes. Place a tablespoon of hazelnut spread in the center, then cover with the mixture up to about 3/4 of the height of the dish or ring. Bake in the preheated oven for about 10 minutes, or until the sides are set and the center is slightly jiggly.