Cut pancetta into 1-inch (2.5 cm) pieces.
Trim bottom end of fennel bulb and cut off stalks; discard.
Cut fennel bulb lengthwise in half, then slice crosswise.
Clean and trim mushrooms; cut into quarters.
Quarter onions.
Trim any fat or gristle from veal.
Mince garlic.
Heat oven to 325°F (160°C).
Heat butter and oil in large skillet over medium heat.
Add veal in single layer; cook until deep brown, about 4 minutes per side.
Remove veal to large shallow casserole.
Add pancetta to drippings in skillet.
Saute over medium heat 3 minutes.
Add onions, fennel, mushrooms and garlic; saute until onions are light brown, about 5 minutes.
Add broth, wine, tomato paste, salt and pepper.
Heat to boiling, stirring and scraping up brown bits which cling to bottom and sides of skillet.
Pour vegetable-broth mixture over veal in casserole.
Bake covered until veal is tender, 30 to 45 minutes.
Remove veal from casserole to deep, heatproof serving dish; keep warm.
Transfer vegetable-broth mixture back to skillet.
Mix flour and water in cup until smooth.
Stir into vegetable mixture; cook, stirring constantly, over medium heat until sauce thickens and bubbles for 1 mintue.
Pour vegetable sauce over veal.