You can find this recipe from River Cottage Every Day by Hugh Fearnley-Whittingstall. The only tweaking I've done is to bake it longer. It has the consistency of a molten cake. If you want a firmer cake add another 1/4 to 1/3 cup of almond meal.
Easy Rich Chocolate Cake
8 oz dark chocolate (60% to 70% cocoa works well)
1 cup (2 sticks) unsalted butter
1/2 cup fine sugar (sometimes called superfine)
1/2 cup light brown sugar
4 medium eggs, separated
1/4 cup all purpose flour
1/3 cup almond meal
whipping cream for garnish
1)Preheat oven to 325 degrees and grease a 10 inch spring form cake pan, lining the base with baking parchment. You can use smaller pans or even ramekins, but watch them carefully, they bake quicker.
2) Melt the chocolate and butter in a double boiler on low heat. Stir occasionally until melted. Take off heat and allow to cool for 10-15 minutes.
3) Beat egg yolks and sugars.
4) When the chocolate and butter has cooled slowly drizzle it into the yolk mixture and mix thoroughly.
5) Fold in the flour and almond meal.
6) In a separate bowl, whisk the egg whites until they hold firm peaks. Adding the egg whites in 3 batches, gently fold them into the chocolate mixture. I've tried to show you the folding motion, but for more details watch the video from Allrecipes.com. It also shows you how to separate eggs and beat egg whites. http://allrecipes.com/video/76/folding-egg-whites/detail.aspx
7) Pour the batter into the pan and bake for 35-40 minutes for a 10 inch pan and approximately 25 minutes for ramekins.
8) Let cool for 10-15 minutes before releasing from the pan. Serve with whipped cream. And for an extra special touch garnish with raspberries.