Preheat oven to 375-400 degrees F.

Grease the bottom and sides of six 6- or 8-ounce ramekins with butter and coat with cocoa powder.

In a medium bowl, melt the chocolate and butter in 1-minute increments in the microwave until smooth.

Off the heat, stir in salt and vanilla. Allow the mixture to cool to room temperature.

In a large bowl, beat the eggs and egg yolks together until thick and light in color (2-3 minutes).

Add powdered sugar and mix until combined.

Add the cooled chocolate mixture and the flour, mixing just until combined.

Divide the batter among the ramekins and place on a baking sheet.

Bake for 12-13 minutes until the sides are set but the center is soft.

Allow to sit for 2-3 minutes before loosening the edges with a knife.

Invert the ramekins onto plates and serve dusted with powdered sugar or with toppings.