Add the olive oil to a very large pot over low heat and cook the onions until they are deep brown and caramelized, which takes about 30 to 40 minutes.
Add the garlic and cook for 3o to 45 seconds or until fragrant.
Deglaze with red wine and cook over low to medium heat until the amount of liquid is reduced by one-half, about 5-7 minutes.
Place in the sausage and ground sirloin and cook over medium heat until cooked throughout. There should be no pink while stirring often to break up any large chunks.
While the meat is cooking, crush the whole peeled tomatoes with your hands to bite-sized pieces.
Put in the tomatoes, oregano, and basil and cook over low heat for 30 minutes.
Finish by stirring in the cheeses, parsley, and balsamic vinegar and adjusting the seasonings with salt and pepper and sugar, if needed.
Lastly, thicken it by stirring in tomato paste until it is to your desired thickness. This is optional.
Toss with cooked spaghetti and serve.
Notes
Make-Ahead: You can make this up to 2 days before serving it. Keep it in the refrigerator until 1 hour before serving it, and reheat it in a large pot until it is hot.How to Store: To store the spaghetti sauce, cool it in an ice bath in your sink or transfer it to a refrigerator and cool it uncovered until it is cold, which takes about 3-4 hours. Cover it and keep it in there for up to 5 days. This will also freeze, covered for up to 3 months. Thaw for 1 day in the refrigerator before reheating.How to Reheat: Add your desired amount to a medium-size pot and cook over low heat until hot. You can also reheat in a microwave-safe bowl until hot.This recipe makes a lot, so please hover your mouse over the serving amount and scale it up or down to fit your desired needs.The difference between a spaghetti sauce and a marinara sauce is that marinara is vegetarian and has fewer ingredients. While a spaghetti sauce can also be meatless, it tends to have a few more items.Just like with soup, this sauce will get better with time. It can simply be ready to eat in under 70 minutes, but if you let it simmer for several hours over low heat, the ingredients will have more time to infuse, making the overall flavor more intense and delicious. It will be far better to wait that long the next day.If you like an extremely thick sauce, I recommend stirring in 3 to 4 tablespoons of tomato paste once it is finished cooking.