Preheat the oven to 170 degrees Celsius. Line a 2lb loaf tin with a loaf tin liner or baking paper.
In a large bowl, cream together the butter and sugar until light and fluffy.
Beat in the eggs one at a time, until fully combined.
Fold in the flour, making sure that it is all mixed in well.
Zest the lemon. Add this to the bowl along with the sultanas. Stir until they are fairly evenly distributed.
Spoon the mixture into the loaf tin. Put it into the oven for one hour, until risen, golden and a skewer inserted into the middle comes out clean.
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Notes
This loaf cake will keep for up to a week in an airtight container in a cool, dry place. Alternatively, allow the cake to cool after cooking then wrap well and store in the freezer for up to three months. Defrost thoroughly before eating.