Liquid cream, vanilla ice cream or banana to accompany.
Grease 8 medium soufflé baking dishes or pans with a bit of oil and put them into the oven.
Preheat oven to 220°C.
Mix chocolate and butter in a bowl and microwave it for 1 minute at maximum power (if butter is not fully melted, heat in the microwave some more). Mix well with a stick or fork, until you are sure there are no chocolate lumps left.
Add sugar and mix until you get a uniform pastry. Incorporate the eggs and flour and mix everything very well.
Fill baking dishes or pans with the mixture, but not to the top, because it will rise a bit. Put them into the oven for 10 minutes, so as to cook just on the outside, remaining liquid inside.
Take the volcanoes out of the oven and let them rest for a while until cooler. Unmold very carefully; if necessary, run a knife around the edge to loosen them. Put the volcanoes upside down on a large dish or individual dessert dishes and decorate with vanilla ice cream, whipped cream or banana.
The pastry may be prepared the day before; if so, fill baking dishes or pans, cover with plastic film and put them into the fridge. Calculate an hour before eating, take out of the fridge and then bake.