Preheat your oven to 425°F. Spray six 6-ounce ramekins with baker's spray, then dust them with cocoa powder. Place them on a baking tray for easy handling.

In a microwave-safe bowl, combine the chocolate pieces and butter. Heat in the microwave for 1 minute, then stir. If not fully melted, continue heating in 15-second intervals, stirring in between.

Stir the vanilla extract into the melted mixture. Add the powdered sugar and mix well until smooth. Beat in the whole eggs one at a time, followed by the egg yolks.

Incorporate the salt and flour into the batter, mixing just until blended. Divide the batter evenly into the prepared ramekins, filling each about ⅔ full.

Bake the cakes for 12 to 14 minutes. They should appear firm around the edges but the centers should look slightly undone. Let them cool for 2 minutes, then carefully invert each onto a plate. Garnish with a dusting of powdered sugar before serving.