1. In a large pot, heat the olive oil over medium-high heat. Season the beef cubes with salt and pepper, then brown them on all sides. Remove the beef from the pot and set it aside.

2. In the same pot, add the onion, garlic, carrots, and celery. Cook until the vegetables are softened, about 5 minutes.

3. Return the browned beef to the pot. Stir in the potatoes, apple cider, beef broth, Worcestershire sauce, thyme, and bay leaves. Bring the mixture to a boil.

4. Reduce the heat to low, cover the pot, and simmer the stew for 1.5 to 2 hours, or until the beef is fork-tender.

5. Stir in the cornstarch mixture and cook for an additional 5 to 10 minutes, until the stew has thickened to your desired consistency. Remove the bay leaves before serving.

6. To make creamy mashed potatoes, peel and cut the potatoes into 1-inch cubes. Place them in a large pot and cover them with cold water. Bring the water to a boil and cook the potatoes until they are fork-tender, about 15-20 minutes. Drain the potatoes and return them to the pot. Add butter, milk, salt, and pepper to the pot, and mash the potatoes until they are smooth and creamy.