Melt butter in a large saucepan or flameproof casserole over medium heat. Add leek, parsnip, carrots and onions or shallots. Stir in stock, sugar, bay leaf and pepper. Bring to the boil, cover and reduce heat to low.
Cook for 10 minutes or until vegetables are barely tender. Remove lid and boil liquid for 2 to 3 minutes or until bubbling and reduced to a thick syrup-like glaze. Toss vegetables in the glaze. Discard bay leaf and serve immediately.