Sauté Aromatics: Heat olive oil in a large saucepan over medium heat. Add onions and garlic, sauté until translucent (2-3 mins). Add grated carrot (if using) and cook for another 2 mins.
Brown Meat (Optional): Add ground beef/sausage, breaking it apart with a spoon. Cook until browned (5-6 mins). Drain excess fat if needed.
Simmer Sauce: Stir in crushed tomatoes, tomato paste, water/broth, sugar, salt, pepper, oregano, basil, red pepper flakes, and bay leaves. Bring to a boil, then reduce heat to low.
Cook: Simmer uncovered for 25-30 mins, stirring occasionally, until thickened. Remove bay leaves.
Blend (Optional): For a smoother sauce, blend briefly with an immersion blender.
Serve: Toss with cooked spaghetti, garnish with fresh herbs, and top with grated Parmesan.
