Heat the oven to 180C/160C fan/gas 4.
Beat together the butter and caster sugar until pale and creamy, then add the eggs, one at a time, slowly mixing through.
Sift in the self-raising flour, then add the lemon zest and mix until well combined.
Line a loaf tin (8 x 21cm) with greaseproof paper, then spoon in the mixture and level the top with a spoon.
Bake for 45-50 mins until a thin skewer inserted into the centre of the cake comes out clean. While the cake is cooling in its tin, mix together the lemon juice and caster sugar to make the drizzle.
Prick the warm cake all over with a skewer or fork, then pour over the drizzle – the juice will sink in and the sugar will form a lovely, crisp topping.
Leave in the tin until completely cool, then remove and serve. Will keep in an airtight container for 3-4 days, or freeze for up to 1 month.