1 grapefruit
1 grapefruit, juice only
225g/8oz caster sugar
50²µ/1ΒΎ΄Η³ϊ caster sugar
225g/8oz self-raising flour
1 tsp vanilla extract
225g/8oz unsalted butter, softened, plus extra for greasing
4 free-range eggs
1–2 tbsp milk