Prepare the Meatballs:

1. Preheat the oven to 350°F and position the rack in the middle.
2. In a large bowl, whisk together the egg, parsley, tomato paste, oregano, salt, pepper, garlic, and water.
3. Add the ground beef, ground pork, bread crumbs, and Parmigiano-Reggiano. Mix gently until just combined—do not overwork the mixture.
4. Roll into golf ball-sized meatballs and place them on an ungreased baking sheet.
5. Bake for 10 minutes, then flip the meatballs and bake for an additional 10 minutes, until browned and nearly cooked through.

Make the Sauce:

1. In a large skillet, melt butter over medium heat. Add the onion and sauté for 5 minutes until softened.
2. Stir in garlic and cook for another minute until fragrant.
3. Pour in the marinara sauce, bring to a gentle simmer, and stir in sugar, salt, and pepper.
4. Add heavy cream and simmer for 2-3 minutes to blend flavors.
5. (Optional) In a small bowl, mix ¼ cup water with 1 tbsp flour to create a slurry, then whisk it into the sauce to thicken.
6. Stir in the garlic powder, paprika, salt, and pepper.

Combine & Serve:

1. Cook spaghetti according to package instructions.
2. Add drained spaghetti directly into the sauce, stirring occasionally for 5 minutes to let the pasta absorb flavor.
3. Add the baked meatballs into the skillet and gently toss to combine.
4. Serve hot, garnished with extra Parmigiano-Reggiano.