Heat oven to 450°F (230°C).
Butter two 4-oz ramekins, dust with flour, and tap out excess.
Melt chocolate (microwave or double boiler). Stir in butter until smooth.
In a separate bowl, whisk egg, yolk, and sugar until pale.
Stir egg mixture into melted chocolate, add flour, and whisk to combine.
Divide batter between ramekins. Place on a baking sheet.
Bake 6–8 min until tops are set but centers still jiggle.
Invert onto plates, gently lift ramekins, and serve immediately (ice cream optional).
