Simple Chestnut and Sage Soup - River Cottage

Ingredients

• 3 tablespoons olive oil, plus extra to trickle
• 15g butter
• 1 medium onion, chopped
• 6 sage leaves, roughly chopped, plus extra to finish
• 1 small garlic clove, finely chopped
• 1 litre vegetable stock
• 400g cooked, peeled chestnuts
• 100ml crème fraîche
• Sea salt and freshly ground black pepper