Cook spaghetti in a large pot of salted water until al dente. Reserve 1 cup of pasta water. Drain well but do not rinse.
In a large bowl, combine the ground beef, egg, breadcrumbs, parsley flakes, ground rosemary, salt, and pepper. Mix until well combined.
Make sauce. In a separate bowl, whisk together the tomato puree, dried oregano, dried basil, salt, pepper (optional), and 1 cup of reserved pasta water until smooth.
Preheat your oven to 355℉ (180℃).
Place the tart pan on a baking sheet to catch any spills.
Spread the cooked spaghetti evenly in an 11-inch (27cm) tart pan.
Form small meatballs (about the size of a marble or grape) from the ground beef mixture and place them on top of the spaghetti.
Pour the tomato sauce evenly over the meatballs and spaghetti.
Place the tart pan on the baking sheet to avoid any spilling in the oven.
Bake for about 20 minutes, or until the meatballs are golden brown and fully cooked in the center.
Let the dish cool slightly. Then, place a small dollop of sour cream on each meatball, followed by a green pea on top to create an "eye" effect.