(click on the text to highlight each stage):

1. Heat the oven to 170°C, 325°F, gas 3. Grease a large loaf tin.
2. Beat the butter, half the sugar, nutmeg and salt in a mixing bowl until creamy. Split the vanilla pod and scrape out the seeds into the mixture.
3. Beat in the egg yolks one at a time until the mixture is smooth.
4. Whisk the egg whites with the remaining sugar until stiff.
5. Stir together the ground almonds, flour, potato flour, baking powder and cranberries in a bowl. Add half the mixture to the mixing bowl and stir well.
6. Whisk the egg whites until stiff but not dry and fold into the mixutre until incorporated. Gently stir in the remaining flour mixture.
7. Spoon into the loaf tin and bake for 45-55 minutes until risen and golden. Insert a skewer into the centre of the cake, which should come out clean.
8. Cool in the tin for 10 minutes, then turn out onto a wire rack to cool.
9. For the icing: sift the icing sugar into a bowl and stir in the cranberry juice and a little colouring if liked. Spread the icing on top of the cake and leave to set.