½ lemon, juice only
2 lemons, zest only
12-15 large ripe plums, stones removed, chopped
100²µ/3½´Ç³ú rolled porridge oats
175g/6oz plain flour, sifted
160²µ/5½´Ç³ú caster sugar
50g/2oz caster sugar
50g/2oz dark muscovado sugar
butter, for greasing
100²µ/3½´Ç³ú butter, chilled, cut into cubes
custard, to serve