Pat shanks dry with paper towel to remove moisture; using twine, circle circumference of each shank and tie tightly with twine
Season each shank with salt and freshly ground pepper; dredge each in flour, shaking off excess
In a large heavy pot, heat oil and butter until smoking; add tied veal shanks to hot pan
Brown all sides (3 minutes per side); remove browned shanks and reserve
Preheat oven to 300F
In the same pot, add onion, carrot and celery; season with salt to draw out moisture from vegetables
Saute until translucent; about 8 minutes
Add veal jus cubes until melted; combine
Add white wine and reduce liquid by half (5-8 minutes); add beef stock
Return shanks and juices to pan with stock; bring to boil
Place shanks, uncovered in oven for 3 hours; cooking liquid should be about 3/4 up each shank (add more stock, if necessary, or cover with foil or lid
Carefully remove cooked shanks; place in decorative serving platter; cut off and discard twine
Set pot with juices and sauce on stove; bring to a boil and reduce by 1/3 or ½
Sprinkle 1 tablespoon corn starch into sauce to thicken; stir constantly
Season with salt and pepper; pour over shanks and place remainder in pitcher alongside
Garnish with chopped parsley and lemon zest
Traditionally served over risotto; mashed potatoes also make a wonderful accompaniment