Place the beetroot, carrot, parsnip, leek, onion, lemon juice, spices and bay leaves in a large saucepan with the stock. Bring to the boil, then reduce the heat to low and simmer, partially covered, for 2 hours. Cool slightly, then blend in batches and season well with salt and pepper. Return to saucepan and gently heat through. Place in bowls and garnish with sour cream and dill. Serve with rye bread.