1. In a large skillet, heat the olive oil over medium heat. Add the onion and garlic and sauté until the onion is translucent.

2. Add the ground beef to the skillet and cook until browned, breaking it up with a spoon as it cooks.

3. Transfer the cooked beef mixture to the slow cooker.

4. Add the crushed tomatoes, tomato paste, oregano, basil, salt, pepper, beef broth, Worcestershire sauce, and bay leaf to the slow cooker. Stir to combine.

5. Cover and cook on low for 6-8 hours or on high for 3-4 hours.

6. About 20 minutes before serving, cook the spaghetti according to package instructions.

7. Discard the bay leaf from the sauce. Serve the Bolognese sauce over the cooked spaghetti and top with freshly grated Parmesan cheese.

For a healthier twist, you can substitute ground turkey or chicken for the ground beef. If you have picky eaters, try finely grating some carrots or zucchini into the sauce for added nutrition without altering the flavor much. For a vegetarian version, use lentils instead of meat and vegetable broth instead of beef broth. You can also add a splash of red wine to the sauce for a richer flavor. If you prefer a spicier kick, add a pinch of red pepper flakes.