Preheat the oven to 200°C/392°F (without fan).
Place a baking tray in the middle of the oven.
Use the softened butter to generously grease 6 ramekins. I use ramekins with a capacity of 250 ml/1 cup.
Melt the butter and chocolate in a small bain-marie (bowl over pan of simmering water), or on low power in the microwave at short intervals.
Whisk the chocolate mixture together and set aside to cool slightly.
In a medium-sized mixing bowl, whisk together the eggs, sugar, flour and salt.
Whisk in the chocolate mixture until everything is well-combined.
Pour the batter in equal quantities into each ramekin, about half way.
Place the ramekins into the oven and bake for 10-12 minutes. Please see Kitchen Notes below for tips.
The Chocolate Fondants are ready when they have puffed and risen slightly with a cracked topping, but the centers are still molten.
If desired, dust with cocoa powder or icing sugar (powdered sugar).
Serve immediately.