Beat the butter (or margarine) with the sugar and lemon rind until fluffy. Add in the eggs one by one, mixing well after each addition. Fold in the flour and milk with a spatula.
Pour the mixture into a loaf tin lined with greaseproof paper and bake in a cold oven for 55 minutes to 1 hour at 180°C/350°F/gas mark Do not preheat the oven. The cake will bake as the temperature rises.
When done, remove cake from the oven and prick all over with a skewer.
Stir the lemon sauce ingredients together briskly until sugar dissolves.
Pour over the hot cake. Leave cake to set overnight (ideally for 2 days) before cutting. (The freshly-baked cake will crumble when you cut it.)
Note: This recipe has been in the Kenton family for half a century. The cake is best eaten after 1-2 days and its sweet and tart flavours are accentuated by the lemon sauce.