Chickpea Purée with Red Onion and a Parmesan and Garlic Crust

• 275 g/10 oz dried chickpeas
• 1 medium red onion

Soak the chickpeas in plenty of cold water overnight. Drain, put in a saucepan and cover generously with water. Boil until completely soft.

Meanwhile, peel the onion, cut in half and slice finely. Melt a third of the butter with half the olive oil in a frying pan over a medium heat. Add the sliced onion and cook, stirring, until soft but not browned. Stir in the caster sugar, remove fro