Melt the chocolate and butter together in a heatproof bowl set over a saucepan of gently simmering water, or in short bursts in the microwave. Stir until smooth.

In a large bowl, whisk the eggs and sugar until combined. Add the melted chocolate mixture and whisk until smooth. Add the flour and salt and stir just until incorporated.

Divide one-third of the batter among the prepared ramekins. Place 1 tablespoon/15 grams hazelnut spread in the center of each, then cover with the remaining batter, filling the ramekins about three-quarters full.

Bake until the edges are set and the centers still have a slight wobble, about 10 minutes. Serve hot.