Steps
1. Preheat your oven to 200°C (390°F).
2. Grease a ramekin with butter and dust with flour, ensuring the sides are coated.
3. In a heatproof bowl, melt the dark chocolate and butter together over a pot of simmering water (double boiler method), stirring until smooth.
4. In a separate bowl, whisk the egg and sugar together until pale and fluffy.
5. Gently fold the melted chocolate mixture into the egg mixture.
6. Sift in the flour and salt, folding until just combined.
7. Pour the batter into the prepared ramekin and bake for 10-12 minutes, until the edges are set but the center is still soft.
8. Let it cool for a minute, then carefully invert onto a plate. Serve warm, optionally with a scoop of vanilla ice cream.