Preheat your oven to 425°F. Grease very well the entire insides of 4 4-ounce oven-safe ramekins, and set them in a casserole dish with at least 2 inch high sides, and set aside.

Melt the chocolate and 4 tablespoons butter together in a double boiler or a microwave-safe bowl (melt at 70% power in 30 second intervals, stirring in between, until melted and smooth), stirring frequently until just melted. Set the chocolate mixture aside.

In a large bowl, place the eggs, egg yolks, sugar and vanilla, and whisk to combine. The mixture will be very yellow in color and thin in consistency.

Whisk vigorously (this can be done more easily with a mixer) until the mixture is very pale yellow in color and thickened in consistency.

Drizzle the chocolate and butter mixture into the large bowl with the thickened egg mixture, whisking constantly until combined.

Add the flour, cocoa powder and salt, and whisk to combine well. The mixture will be somewhat thick, but pourable and smooth. Pour the mixture carefully into the 4 prepared ramekins, filling each ¾ of the way full. (See Recipe Notes for make-ahead instructions.)

Place the casserole dish with the filled ramekins on the bottom rack of the preheated oven, and carefully fill the casserole dish with cool tap water until the water reaches about halfway up the sides of the ramekins.

Close the oven and bake until the tops of the cakes are set and are just beginning to pull away from the sides of the ramekins, about 15 minutes.

If you used smaller ramekins, bake for a few minutes less; larger ramekins will take a few minutes more.

Remove the dish from the oven and lift the ramekins out of the casserole dish with tongs. The water bath will be boiling, so move carefully and deliberately.

Place the ramekins on a wire rack to cool for about 10 minutes before turning each cake out onto a small plate, and dusting with confectioners’ sugar. Serve immediately.