Caroline Dumas’ Cream of Jerusalem Artichoke, Fennel, and Celeriac Soup

Ingredients

• • 2 tablespoons olive oil
  • 1 leek or 1 onion, thinly sliced
  • 1 1/2 cups (375 ml) diced Jerusalem artichoke
  • 1 1/2 cups (375 ml) fennel pieces
  • 1 1/2 cups (375 ml) diced celeriac
  • 6 cups (1.5 litres) boiling water
  • 1/4 cup (60 ml) 35% cream (optional)
  • Fennel leaves
  • 1 tablespoon lemon oil (optional)
  • Sea salt and freshly ground pepper