Steps
Preheat your oven to 425°F (220°C).
Grease a ramekin with butter and dust it with cocoa powder (optional).
In a microwave-safe bowl, melt the dark chocolate and butter together in 30-second intervals, stirring until smooth.
In a separate bowl, whisk the egg and granulated sugar until combined.
Add the melted chocolate mixture to the egg mixture and stir until well combined.
Fold in the flour, vanilla extract, and a pinch of salt until just combined.
Pour the batter into the prepared ramekin.
Bake for 12-14 minutes until the edges are firm but the center is still soft.
Let it cool for a minute, then invert onto a plate and enjoy while warm.