Chocolate fondant has a bit of a reputation for being difficult, mainly because whenever contestants on cooking shows like Masterchef try it, they tend to fail. The reason is simple: chocolate fondant needs to be baked so that the exterior is firmly set, while the centre is still gooey and delicious, and if you don't know your oven it's very difficult to pull off.
Preheat your oven to 220°C (428°F). Heat some water in a pan until boiling, then turn down to simmer. Place a colander over the water, and place the butter and chocolate (broken into small pieces) over it. Whisk the whole egg and the egg yolk in a bowl, then whisk in the sugar and the cocoa powder. When the butter and chocolate have melted, whisk those in, and finally whisk in the flour.
Grease the inside of 2 small steel pudding tins or ramekins, and then sprinkle the inside and bottom of each on with cocoa powder. Pour half of the pudding mixture into each container.
At this point, you can refrigerate the puddings until you are ready for them, or you can bake them straight away.
The cooking time and temperature are crucial to the success of your fondants, and you might have to experiment with making a fewbefore you find the right combination. I've seen recipes that suggest 10 minutes at 200°C (392°F), but my oven takes 15 minutes at 220°C (428°F).
Once the fondants are cooked, use a knife to loosen the edges, and then tip them out onto a plate. Serve with Chantilly cream or ice cream.