01 - Preheat the oven to 390°F. Grease four 6 oz ramekins with butter and lightly dust with flour, tapping out the excess.
02 - In a heatproof bowl set over simmering water, melt the chocolate and butter together, stirring until smooth. Remove from heat and allow to cool slightly.
03 - In a separate bowl, whisk the eggs, egg yolks, and sugar until the mixture is pale and thick, approximately 3 minutes.
04 - Fold the melted chocolate mixture gently into the egg mixture until fully integrated.
05 - Sift the flour and salt into the mixture, then gently fold them in until just combined.
06 - Evenly distribute the batter among the prepared ramekins. Place them on a baking tray and bake for 10 to 12 minutes, until the edges are set but the centers remain soft.
07 - Allow cakes to cool for 1 minute, then run a knife around the edges and invert each cake onto a serving plate. Dust with powdered sugar and serve immediately with vanilla ice cream or whipped cream if desired.