Preheat the oven to 425°F. Generously butter 6 (6-ounce) ramekins.
Melt the morsels and the 3/4 cup butter in a small saucepan over medium-low heat, whisking frequently until the morsels are completely melted and the mixture is smooth, about 5 minutes. Let cool for a couple of minutes, whisking to keep it all smooth.
Whisk together the eggs, egg yolks, vanilla, sugar and salt until thick and pale yellow, about 4 minutes. Whisk in the flour, then the melted chocolate mixture, until well incorporated.
Distribute the mixture evenly between the ramekins, filling them about 4/5 full. Bake for 10 minutes until the cakes are just kind of set, but the are still jiggly when you wiggle the pan. You may well see some of the molten interior peeking out of the top. It's beautiful.
Turn the cakes over onto a serving platter or individual plates, and using a little sieve dust over the confectioners' sugar if desired.