Preheat oven to 450 degrees. Butter and lightly flour (with all purpose flour or tapioca flour) 6 6-ounce ramekins. Turn the ramekins upside down and tap to release excess flour. Arrange on a rimmed baking sheet.

In a double boiler or heatproof bowl set atop a saucepan of simmering water, melt the butter and chocolate and whisk until combined.

With a mixer, beat the eggs, egg yolks, sugar, salt and vanilla or peppermint extract at high speed until thickened and lighter in color.

Lower the speed down to medium, and slowly pour the chocolate mixture into the egg mixture. Then add the flour until just combined. At this point the batter can be prepared several hours in advance and refrigerated. Bring to room temperature before baking. Or leave at room temperature for up to two hours.

Transfer the batter into a cup with a lip and evenly pour the batter into the prepared ramekins. Bake for 12-13 minutes, or until the sides of the cakes are firm, but the centers are still soft.*

Allow the cakes to cool in the ramekins for 1 minute. Run a thin knife around the edge of each ramekin. Cover each with a dessert plate and carefully flip over and unmold. Serve immediately.