In a large mixing bowl combine the pork, veal and beef and season with salt and pepper, to taste. Mix in the garlic, parsley, thyme, basil and bread crumbs until well combined.
When thoroughly mixed, slowly add the beaten eggs and mix well. Add in the milk and again mix thoroughly. Let rest, covered, in the refrigerator for 1 hour. (See Cook's Note)
While the mixture is resting in the refrigerator, take another bowl and mix the already cooked and cooled spaghetti with a little of the marinara sauce and season with salt and pepper, to taste.
Remove the meat from the refrigerator and form into 2-ounce portions. Flatten the meatball and add a small amount of the spaghetti-sauce mixture in the center. Wrap the meat around the filling to form an enclosed meatball. Repeat until all the meat has been used.
Preheat the oven to 350 degrees F.
Return the meatballs to the refrigerator for another hour and allow to rest.
In a large skillet heat the grapeseed oil over medium heat and begin to fry the meatballs until golden brown on all sides. Transfer into an ovenproof serving dish and cover with the remaining marinara sauce. Bake until cooked through, about 15 minutes.
Remove from the oven and serve immediately sprinkled with grated Parmesan.
The mixture should remain tight, so add the milk little by little. If it begins to get too wet, stop adding the milk and reserve in refrigerator until after the mix has rested for 1 hour. Then, if more milk is needed, add it at this time.