Preheat your oven to 425°F (220°C).

Generously grease and flour the ramekins. Tap out any excess flour. Line the bottom of the ramekins with a small circle of parchment paper for an extra layer of protection.

In a double boiler or microwave-safe bowl, combine the chopped chocolate and butter. If using a double boiler, heat over simmering water, stirring occasionally, until melted and smooth. If using a microwave, heat in 30-second intervals, stirring in between, until melted and smooth. Be careful not to overheat the chocolate, as it can seize up.

In a separate mixing bowl, whisk together the eggs, egg yolks, sugar, and salt until pale and slightly thickened, about 2-3 minutes. The mixture should ribbon slightly when you lift the whisk.

Slowly pour the melted chocolate mixture into the egg mixture, whisking constantly until well combined. Be gentle to avoid deflating the eggs too much.

Sprinkle the flour over the chocolate mixture and gently fold it in using a rubber spatula. Be careful not to overmix, as this can develop the gluten in the flour and result in a tough cake. Fold just until the flour disappears.

Divide the batter evenly among the prepared ramekins. Each ramekin should be about ¾ full.

Place the ramekins on a baking sheet and bake for 12-15 minutes. The baking time will vary depending on your oven, so keep a close eye on the cakes. They are ready when the edges are set and the center is still slightly soft. The top should look slightly cracked.

Let the cakes cool in the ramekins for 1-2 minutes.

Run a thin knife around the edges of the ramekins to loosen the cakes. Place a plate over the ramekin and carefully flip it over. Gently tap the ramekin to release the cake.

Dust the cakes with powdered sugar, if desired. Serve immediately while the center is still molten. You can also add a scoop of vanilla ice cream, fresh berries, or a dollop of whipped cream for an extra touch of decadence.