In a large bowl, combine beef, egg, Parmesan, bread crumbs, basil, cream, Italian seasoning, and red pepper flakes (if using); season with salt and black pepper. Using a wooden spoon or your hands, mix until well combined. Using a large cookie scoop or spoon, portion mixture into 15 meatballs (about 3 Tbsp. each).
In a large ovenproof skillet over medium-high heat, heat oil until shimmering. Cook meatballs, turning occasionally, until browned on all sides, 5 to 7 minutes.
Turn on broiler. In a large bowl, crush tomatoes with your hands or a potato masher.
Add tomatoes and their juices, Italian seasoning, and 3 cups water to meatballs; season with salt and black pepper and bring to a simmer. Cook, stirring occasionally, until warmed through, about 5 minutes. Transfer meatballs to a large plate. Add orzo to sauce and cook, stirring occasionally, until al dente, 8 to 10 minutes.
Stir in butter and ½ cup Parmesan until melted. Return meatballs to skillet and top with mozzarella and remaining ¼ cup Parmesan.
Broil, watching closely, until cheese is melted, 2 to 3 minutes. Top with basil.
