Creating the perfect Slow Cooker Beef Manhattan is easy if you follow these steps:

1. Prepare the Beef: Season the beef chunks with salt and pepper.
2. Sear the Meat: In a skillet over medium-high heat, heat the olive oil. Add the beef chunks and sear until browned on all sides. This adds depth to the flavor.
3. Add Onion and Garlic: Once seared, add the diced onion and minced garlic to the skillet. Sauté for 2-3 minutes until fragrant.
4. Transfer to Slow Cooker: Place the browned beef, onions, and garlic into the slow cooker.
5. Combine Remaining Ingredients: Pour in the beef broth, Worcestershire sauce, thyme, carrots, celery, and add the bay leaves.
6. Stir Together: Mix all the ingredients until combined, ensuring the beef is submerged in the broth.
7. Set the Slow Cooker: Cover and cook on low for 6-8 hours or on high for 3-4 hours until the beef is tender.
8. Thicken the Gravy (Optional): If you prefer a thicker gravy, mix cornstarch with a couple of tablespoons of water in a small bowl. Stir this mixture into the cooker during the last 30 minutes of cooking.
9. Check Seasoning: Before serving, taste the gravy and adjust the seasoning with more salt or pepper if necessary.
10. Serve: Remove the bay leaves, and garnish with freshly chopped parsley for a pop of color.

These steps will guide you in creating this incredible dish effortlessly, ensuring a satisfying outcome every time.