Melt 225 g (7½ oz) chocolate with the butter in a bowl over a pan of simmering water (see
Beat the egg yolks and sugar until pale, thick and foamy. Slowly whisk in the melted chocolate. Fold in the flour (and any bran in the sieve) and ground almonds.
Whisk the egg whites in a large grease-free bowl until softly peaking. Beat a large spoonful of the egg whites into the chocolate mixture, to loosen it slightly, then fold in the remainder using a large metal spoon.
Grease a 20 cm (8 inch) springform tin and line with a greaseproof cake liner or nonstick baking paper. Pour the mixture into the tin and bake in a preheated oven, 180°C (350°F), Gas Mark 4, for 45 minutes or until a skewer pushed into the centre comes out clean.
Cool in the tin for 10 minutes, then release and remove the sides of the tin and continue cooling. Grate half the reserved white chocolate (see