Preheat oven to 180C/350F/Gas 4/fan oven 160C.
Butter an 18cm/7in deep round cake tin and line the base.
Melt the chocolate in a bowl over a pan of simmering water.
Beat the sugar and butter until light and fluffy.
Beat in the yolks, one at a time.
Stir in the almonds and chocolate.
Whisk the egg whites in a bowl until stiff peaks form.
Fold a quarter of the egg white into the chocolate mixture, then sift in a quarter of the flour and baking powder.
Repeat three more times until the egg white and flour is evenly mixed in.
Pour the mixture into the tin.
Bake for 35-40 minutes until risen and firm.
Cool for five minutes, turn out on to a wire rack, peel off the paper and cool completely.
I then added some homemade marzipan and melted chocolate to decorate.