The Best Homemade Spaghetti Sauce

1 tablespoon olive oil
2 cups onion, chopped and divided
5 cloves garlic, finely minced
2 pounds lean ground beef or lean ground turkey
1 red bell pepper, seeded, cored and coarsely chopped
1 can (12-ounces) tomato paste
1 teaspoon coarse, kosher salt
1 teaspoon black pepper
3 teaspoons dried oregano
3 teaspoons dried basil
1 1/2 teaspoons dried thyme
2 cans (14-ounces each) Italian-style diced tomatoes or regular diced tomatoes
2 cans (28-ounces each) crushed tomatoes
8 ounces button or baby bella mushrooms, chopped
1 1/2 cups beef stock or beef broth
2 tablespoons brown sugar
2 bay leaves
2 tablespoons balsamic vinegar

DIRECTIONS:

In a large pot, heat the olive oil over medium heat. Add 1 cup of the chopped onions, and sauté until translucent and slightly browned, 3-4 minutes. Add garlic, and cook, stirring constantly for a minute or so.
Add beef, and cook, breaking into small pieces, until it is no longer pink, 6-7 minutes. Drain excess grease.
In a blender or food processor, blend remaining 1 cup onion and the red pepper until smooth. Pour the mixture into the pot with the beef and onions.
Add the tomato paste, salt, pepper, oregano, basil and thyme, and cook for 1 minute, stirring until combined.
Add diced tomatoes, crushed tomatoes, mushrooms (if using), beef broth, and sugar. Stir until combined before adding the bay leaves.
Bring the sauce to a boil, and then reduce to low and simmer for 1 hour, stirring occasionally. Stir in the balsamic vinegar and let the sauce rest for 10-15 minutes (for the flavor to absorb) before serving.

*I’ve also had good success making this in the slow cooker; I brown the meat ahead of time and throw everything (minus the olive oil and balsamic vinegar) in the slow cooker and cook on high for 4-6 or low for 7-9 hours. I add the balsamic vinegar 15 minutes before serving.
This sauce halves (or even quarters) great if you don’t want to make such a large batch. I have never tried canning it (but hopefully will figure out a canning recipe soon!).
Make Ahead Instructions: The sauce can be made 2-3 days in advance and stored in the refrigerator. It also freezes beautifully. My favorite way to thaw/cook the sauce is to throw the heaping frozen mass of sauce in the slow cooker and cook it on low for about 5-6 hours. It thaws and heats up wonderfully well.