I make this with a jar of shop-bought lemon curd, but if you'd like to make your own: whisk together 2 large eggs, the yolks from 2 further large eggs and 150g caster sugar in a heavy-based saucepan. Add the finely grated zest and juice of 2 unwaxed lemons and 100g soft unsalted butter, and put the pan over a medium heat, stirring constantly until thickened. This will take around 5-7 minutes, but keep taking it off the heat at regular intervals during this time. When thickened, pour into a…