Place the butter and dark chocolate in a microwave-safe bowl. Microwave on medium heat for approximately 2 minutes or until completely melted and smooth, stirring as required.
Lightly grease six 175ml ramekins or dariole moulds. Sprinkle the moulds with the cocoa powder and rotate the dishes to evenly coat the sides with the cocoa.
Prepare the barbecue for indirect cooking over medium-low heat (close to 180°C). If using a Weber Q barbecue, set up your barbecue with a convection tray and a trivet.
Using an electric mixer, beat together the eggs and sugar for 3 minutes, or until pale and fluffy. Slowly add the melted chocolate mixture. Sift in the flour and continue beating until combined.
Pour the chocolate mixture into the moulds, filling each mould to ¾. Place a Cadbury Crème egg into each mould. Top with another teaspoonful of the chocolate mixture, or until the egg is completely covered.
Bake the fondants over indirect medium-low heat, with the lid closed, for 20 to 24 minutes, or until a crust has formed on the tops and they are starting to come away from the sides. Remove the fondants from the barbecue and leave to rest for 2 minutes.
Slide a butter knife around the inside of the moulds to loosen the fondant. Turn out onto a plate and serve with whipped cream.