In a medium pot over medium-high heat combine vegetable stock, thyme, parsley and potatoes. Bring to a boil and reduce heat to low. Cook, covered, for about 10 to 20 minutes or until potatoes are tender; drain, reserving stock.
In a small bowl combine cornflour and water; add to stock and cook stirring constantly over medium heat until mixture thickens into a sauce. Serve sauce over potatoes.