Mr. C. chose a favourite chocolate cake for his birthday, a recipe from Claudia Roden's A New Book of Middle Eastern Food. It's Sephardic Jewish in origin, and is best slightly undercooked in order to provide the right degree of squidginess in the middle.
Melt 8oz. best quality bitter chocolate, add 2 tblsps. milk, and beat into 6 egg yolks, 4oz. ground almonds and 6 tblsps. caster sugar. Beat the 6 egg whites until stiff and fold into the chocolate mixture. Pour into a greased/lined tin (preferably springform, about 9", but use a smaller one for a thicker, even squidgier cake) and bake at Gas 4/180C/350F/bottom of the Aga baking oven. Here Ms. Roden and I part company: her instructions say 45 mins. to 1 hour, I give mine 20-25 mins. - it's just a matter of personal taste.
It may not be the prettiest of cakes but it tastes wonderful!