After the veal is browned, drain, and set aside. Add in the onion, pinch of salt and pepper, and cook over medium heat till soft (6-8 minutes). After soft add in the garlic and cook for another minute. Remove from pan and set aside.
Place the veal, onion, and garlic in a large mixing bowl.
For the spinach bring a pot of water to a boil. Next to the pot of water set aside another bowl with cold water and ice cubes.
Add the spinch into the boiling water a couple handfuls at a time and let it cook till wilted (about 30 seconds). Remove and place immediately into the ice water to stop the cooking. Repeat for the remaining spinach.
Remove the spinach from the ice bath and place in a blender and chop to a paste. Add the spinach mixture to the bowl containing the veal and onion. Add in the ricotta, 1 cup of the parmigiano-regiano, and 2 cups of the emmental cheese. Stir to combine everything, cover, and set in the refrigerator for a couple of hours.
After a couple of hours pre-heat your oven to 350 degrees and bring a large pot of water to boil over high heat. Once the water is boiling add in the shells and cook for about 10-12 minutes. Drain and set aside.
Using a spoon fill each of the shells with the mixture and cover with tomato sauce in an ovenproof pan. Cook for 20 minutes.
Spinkle the remaining grated parmigiano-reggiano cheese over the shells, serve, and enjoy.