Heat oven to 450°F (230°C)
Butter two 4-oz ramekins, dust with flour, and tap out excess
Melt chocolate using microwave or double boiler, then 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 and place on a baking sheet
Bake 6–8 minutes until tops are set but centers still jiggle
Invert onto plates, gently lift ramekins, and serve immediately with ice cream if desired
