Preheat and Prep:

1. Preheat your oven to 425°F.
2. Generously butter four ramekins to ensure easy release later.

Melt Chocolate and Butter:

1. In a microwave-safe bowl or using a double boiler, melt the unsalted butter with the semisweet chocolate.
2. Stir until smooth and set aside to cool slightly.

Mix Eggs and Sugar:

1. In a separate bowl, whisk together the whole eggs, egg yolks, granulated sugar, and vanilla extract until the mixture is smooth and slightly pale.

Combine Mixtures:

1. Slowly stir the melted chocolate mixture into the egg mixture until fully incorporated.
2. Gently fold in the sifted flour and a pinch of salt, taking care not to overmix.

Fill Ramekins:

1. Divide the batter evenly among the prepared ramekins, filling each about 3/4 full.

Bake:

1. Place the ramekins on a baking sheet and bake in the preheated oven for 12 minutes.
2. The edges should be set while the centers remain soft and molten.

Serve:

1. Remove from the oven and let the cakes sit for 1 minute.
2. Run a knife around the edges, invert onto serving plates, and dust lightly with powdered sugar if desired.
3. Serve immediately, optionally accompanied by a scoop of vanilla ice cream.