Melt butter in the bottom of a heatproof casserole. Stir in flour and allow to colour, stirring continuously. Place veal in this and brown on all sides. Then add hot water or light stock and stir constantly until liquid comes to a boil. Add bay leaf, and thyme, salt and freshly ground black pepper, to taste, and simmer gently, covered, for 1 hour. Then add mushroom caps, peas, and button onions and small carrots which you have blanched in water. Continue to cook until meat and vegetables are tender.