Heat oil in a large saucepan or Dutch oven over medium-high heat. Season veal with salt and pepper, and saute quickly, stirring to brown the pieces on all sides. Put into a platter.
Reduce heat to medium, add shallots and 3 tablespoons water, saute until water has evaporated, about 1 minute. Add garlic and flour, and cook, stirring, for 1 minute longer. Add wine and simmer for 2 minutes. Add stock, the veal with any juices from platter, sage, and thyme, and bring to a boil. Reduce heat so that stew is barely simmering, cover, and cook for 30 minutes. Add potatoes, cover, and cook for 25 minutes longer, or until meat and potatoes are tender.
Heat a large nonstick skillet over medium-high heat until hot. Add mushrooms, and cook, stirring, for about 3 minutes (if mushrooms stick to the pan, add a tablespoon of water). Add mushrooms to the stew, and stir briefly. Just before serving, remove the thyme sprigs, and stir in chives.