Smoked Italian Spaghetti Sauce

Name: Smoked Italian Spaghetti Sauce
Prep time: 15 min
Cook time: 3 h
Total time: 3 h 15 min
Cuisine: American, Italian
Ingredients: 3 tablespoons olive oil; 1 large onion (diced); 1 pound ground Italian sausage (remove casings if needed) (cut or torn into smaller pieces); kosher salt, pepper, crushed red pepper flakes, Italian seasoning; 7 to 9 cloves garlic (minced); 2 24 ounce jars pasta or marinara sauce (or two 28 ounce cans crushed tomatoes); 1 cup chicken broth (or water); 6 ounces chopped, fresh spinach; 1 cup chopped, fresh basil leaves; 1/2 cup grated parmesan cheese