Add the turnip, potatoes, apple and sage and season with a little salt and pepper. Add the stock. Cover and cook over a low heat/medium heat for 25-35 minutes until the vegetables are softened.
Remove from the heat. Add the cream and place in a food processor and blend until smooth.
Check the seasoning.
Add some parmesan or mature cheddar and serve immediately with garnish of sliced apple and extra parmesan.