1. Preheat oven to 375 degrees.

To make the mashed potatoes:

1. In a large pot, cook the potatoes in salted water until fork tender. Once the potatoes are done, let them cool a bit (just enough so you can handle them) and then peel them.
2. While they are still hot, mash them in a bowl and reserve.
3. In a sauce pan, heat the heavy cream and the cream cheese, whisking until the cream cheese dissolves.
4. Add the heavy cream/cream cheese to the potatoes and mix well until you have a smooth mixture.
5. Season with salt and pepper and reserve.

To make the beef:

1. In a large skillet, heat the butter and sauté the garlic and onions until translucent.
2. Add the tomatoes and the herbs and cook for about 2 minutes.
3. Add the ground beef and cook until browned (about 10 minutes).
4. Add the flour, the parmesan cheese and the crushed tomatoes.
5. Cook until the sauce thickens slightly.
6. Add the egg yolk and season with salt and pepper.
7. Transfer the beef to a seasoned 12-inch cast iron skillet.
8. Top with mashed potatoes and then with the mozzarella.
9. Bake in over for 30 minutes or until the cheese has melted and browned.