In a large skillet, heat a little oil over medium heat. Add the ground beef and cook until browned, breaking it up as it cooks. Drain any excess fat and set the beef aside.

Using the same skillet, add a bit more oil if needed and sauté the diced onion until it’s soft and translucent. Toss in the minced garlic and cook for another 30 seconds to a minute, just until fragrant.

In your slow cooker, combine the browned beef, sautéed onion and garlic, jar of marinara, crushed tomatoes, tomato paste, brown sugar, and all the seasonings (Italian seasoning, salt, black pepper, and red pepper flakes). Stir everything together until well mixed.

Set the slow cooker to low for 7-8 hours or high for 4-5 hours. Stir occasionally if you’re home, but it’s not necessary. The long, slow cooking process will develop incredible depth of flavor.