1 tablespoon extra-virgin olive oil
2 onions, chopped fine
8 oz mushrooms, sliced thin
1 tablespoon minced garlic
1/2 pound Italian sausage
1 1/2 pounds lean (90% or better) ground beef
1 large (24 oz.) can diced tomatoes
2 12 oz cans tomato paste
2 teaspoons dried oregano
11/2 teaspoon dried basil
1 1/2 teaspoons dried rosemary, ground or crushed
1 teaspoon crushed red pepper flakes
1 teaspoon freshly-ground black pepper
3/4 teaspoon salt
2 bay leaves
2 cups sharp cheddar cheese, grated
Heat the oil in a Dutch oven, then saute the onions and garlic. After a couple minutes, add the mushrooms. Cook, stirring frequently, until the onions have softened and started to brown.
Meanwhile, heat a large skillet, then add the Italian sausage and ground beef, crumbling it into small (about 1 inch) chunks. Brown the meat, breaking it into smaller chunks with the side of a spoon.
Add the tomato paste to the Dutch oven with the onions and mushrooms and stir for a minute or so, then add the canned tomatoes. Stir and cook for about two minutes, then add the spices and seasonings, stir and cook for a couple more minutes. Drain the meat and add to the Dutch oven with the sauce. Fill one of the tomato paste cans with water and add to the sauce, stirring it in. Add 1-2 more cans of water. Bring the sauce to a light boil, then reduce heat to a low simmer.
Simmer uncovered for about 20 minutes, then covered for at least an hour (about two hours is better, time allowing), stirring occasionally. Add the cheddar cheese, stir it in and simmer until the cheese is melted and incorporated into the sauce, stirring often.
Serve over spaghetti or spaghetti squash. Top with fresh, chopped basil and/or grated Parmesan cheese if desired.
This sauce freezes up excellently, and stays good for about four months in the freezer.