Heat oil and butter in a large pot (or 6-quart Dutch oven) over medium heat. Add mirepoix and cook until softened, about 8–10 minutes. Press to edges of pot.
Increase heat to high. Add beef to the center of the pot, sear, then break it up and cook until browned, about 5 minutes.
Pour in red wine (or broth/water) and cook until most of the liquid evaporates.
Stir in tomato paste and garlic and sauté 2 minutes. Add crushed tomatoes and cook, stirring constantly, for another 1 minute.
Stir in Worcestershire sauce, bay leaves, seasonings, and cream. If serving immediately, stop here. If simmering, add 1-1/2 cups hot water.
Swap pot to smallest burner. Cover and cook on lowest heat for at least 1-1/2 hours up to 3 hours. If needed to prevent the sauce from sticking, stir occasionally and add more water (1/2 cup at a time).Or transfer everything to a slow cooker and cook on low for 5–6 hours.
When sauce has thickened to the consistency of sloppy joes, it’s ready! Adjust seasoning if needed; I typically add 1/2 teaspoon salt. Add sugar and balsamic vinegar to balance flavors if needed.
Cook spaghetti according to package instructions. Don't forget to salt the water (I add 1 tablespoon salt to 12 cups water). Reserve 1-1/2 cups of pasta water before draining.
Optional: Add cooked pasta directly into bolognese sauce and use tongs to toss until pasta is well coated. Add reserved pasta water as needed to loosen the sauce.
Grate fresh Parmesan on top, add fresh parsley, and enjoy!
Notes
Note 1: Finely dice these veggies so they integrate nicely into the sauce. You can use a food processor. I use about 1-1/4 cup onion, 3/4 cup celery, and 3/4 cup carrots, which is equivalent to 1 large onion, 2–3 celery stalks, and 2–3 carrots.Note 2: Finishing additions (if needed): 2 teaspoons sugar and 2 teaspoons balsamic vinegar.Note 3: Optional serving suggestions: fresh parsley (finely chopped) and freshly grated Parmesan.Make Ahead: The sauce gets better overnight! Cool completely, then refrigerate. Warm on low heat before adding pasta.Storage: Store pasta and sauce separately. Sauce keeps well in the fridge for 3–4 days or in the freezer for up to 3 months.