Steps
1. Preheat the oven to 200°C (392°F).
2. Melt the dark chocolate and butter together in a heatproof bowl over simmering water, stirring until smooth.
3. In another bowl, whisk the egg and sugar until pale and fluffy.
4. Fold the melted chocolate mixture into the egg mixture gently.
5. Sift in the flour and a pinch of salt, and fold until combined.
6. If using, dissolve the gelatin in a small amount of warm water and fold it into the batter for added lightness.
7. Grease a ramekin and dust it with cocoa powder, then pour the batter in, filling it about 3/4 full.
8. Bake for 10-12 minutes until the edges are set but the center is still soft.
9. Let it cool for 1 minute, then invert onto a plate.
10. Serve immediately, optionally garnished with fresh berries.