In a large, heavy saucepan or a dutch oven, heat the olive oil and the butter over medium heat.  Add the carrot, onion and celery and cook until translucent, 5-7 minutes.  Add the garlic and cook until fragrant, another 30-45 seconds.  Add the ground beef and brown, breaking it up as it cooks, until cooked through, about 10 minutes.

Stir in the tomato paste and let it cook for a minute or two.  Add in the milk and beef stock.  Bring the mixture to a bubble, then turn the heat down to medium-low and let it simmer for 1 to 1 1/2 hours, until thick.  Add salt and pepper to taste, then remove from the heat and allow it to slightly cool.

Preheat the oven to 400ºF.  Bring a large pot of water to a boil then salt generously.  Add the manicotti and cook according to the package directions.  Drain and reserve.

In a large bowl, combine the cooled ragu, 1/2 cup grated Parmesan, eggs, ricotta, ham and parsley and mix well.  Season with salt and pepper.  Transfer the mixture to a large ziplock bag.

Spray a 9x13” baking dish with nonstick cooking spray.  Spread 1/2 cup of the marinara in the bottom of the dish. 

Cut the corner off of the ziplock bag and fill each of the manicotti shells with the filling, setting them in the dish as they are filled.  Pour the remaining marinara over the shells and top with additional Parmesan cheese.  Place the dish in the preheated oven and bake for 15-20 minutes, or until the cheese is melted and the sauce is hot and bubbling.