Preheat oven to 425 degrees. Butter six (6 oz.) ramekins and transfer to a baking sheet (or butter 6 wells of a jumbo muffin pan). Lightly dust with a little flour, shake out excess.
In a medium saucepan bring about 1-inch of water to a simmer over medium-high heat. Add chocolate and 3/4 cup butter to a heat proof glass bowl. Reduce heat to medium-low, set bowl over saucepan and stir constantly until chocolate and butter have melted. Remove bowl from heat, let rest 5 - 10 minutes until cool.
Stir in powdered sugar and salt until well blended (it will be thick at this point).
Mix in eggs, egg yolks and vanilla (it will take a bit of stirring to get them fully incorporated).
Sift in flour then stir and fold mixture until combined.
Divide batter among prepared custard cups or muffin wells, filling each about 2/3 full (about 1/2 cup in each. If using custard cups transfer them to a baking sheet to bake).
Bake in preheated oven until edges are set but center is still soft, about 11 - 12 minutes.
Remove from oven and cool 1 - 2 minutes. Run a knife around edges to ensure they are loose, then invert onto dessert plates (if using a muffin pan invert onto a cutting board or baking sheet then transfer to individual dessert plates).
Always serve warm shortly after baking. If desired serve with ice cream, whipped cream, or raspberries/strawberries if desired.