Heat the oven to 180C/160C fan/gas 4 and butter and line a 1-litre loaf tin.

Beat the butter and sugar in a bowl for 8 mins until fluffy and very pale. Beat in the eggs one at a time. Fold in the flour, baking powder, bicarbonate of soda and salt, then the soured cream and zest. Spoon into the tin and bake in the centre of the oven for 45-50 mins, or until a skewer inserted into the middle comes out clean. Leave to cool slightly in the tin, then turn out onto a rack to cool completely.

To make the icing, combine the sugar and juice and spoon over the cake. Sprinkle over the pistachios and candied peel, if using (see tip, below). Will keep in an airtight container for up to three days.