Steps
1. Preheat your oven to 425°F (220°C) and grease a ramekin with butter.
2. In a microwave-safe bowl, melt the dark chocolate and butter together in 20-second intervals until smooth.
3. In another bowl, whisk the egg, egg yolk, and sugar until well combined and slightly frothy.
4. Stir the melted chocolate mixture into the egg mixture until smooth.
5. Gently fold in the flour and salt until just combined.
6. Pour the batter into the prepared ramekin, filling it about 3/4 full.
7. Bake in the preheated oven for 12-14 minutes, until the edges are firm but the center is soft.
8. Let it cool for 1 minute, then carefully invert onto a plate.
9. Serve immediately with a scoop of vanilla ice cream on the side.