Peel and chop the onion. Chop the sage and grate the zest of the orange. Put the slices of bread to soak in the milk.
In a salad bowl, combine the veal, the zest, the sage, the bread crumbs and the polenta. Season generously and knead well with your hands. Shape pellets about 50 to 60 g between the palms.
In a pan, sweat the onion with the olive oil. Add the meatballs and brown them on all sides over medium heat. Deglaze with marsala, reduce, then pour the tomato coulis. Cook covered for 25 minutes.
Finish cooking uncovered if necessary to concentrate the sauce.
Enjoy hot with spaghetti.