Grease and greaseproof-paper line a 9 inch springform pan.
Using an electric beater, beat together cake ingredients for about 2 minutes, until well combined. Spoon into pan.
Bake for 35 minutes, until well-risen and when a skewer is inserted in the middle, comes out clean. Remove from heat. Allow to cool in the tin for 10 minutes. Turn out onto a wire rack and allow to cool completely.
Place chocolate and cream in a saucepan and heat gently, stirring occasionally, until chocolate is melted. Remove from heat and allow to cool for 5–10 minutes. Pour over cake and spread over top and sides. Leave until set.