Cut the beef into large bite-sized chunks. If the pieces are too small, they will dry out during the long cooking process. Pat the meat dry with paper towels. This step is crucial for achieving a good sear. Season generously with salt and black pepper.

Heat a little oil in a large heavy-bottomed pot over medium-high heat. Add the beef in batches. Do not overcrowd the pot, or the meat will steam instead of brown. Sear the cubes on all sides until they are nicely caramelized. Remove the browned beef and set it aside on a plate.

In the same pot, add the chopped onion, garlic, carrots, and bell pepper. The moisture from the vegetables will help lift some of the flavor from the bottom of the pan. Cook for 5 to 7 minutes until the onions are translucent and the vegetables have softened slightly.

Stir in the tomato paste. Let it cook for 1 to 2 minutes. This caramelizes the sugars in the paste and removes any raw metallic taste, adding a deep savory note to the stew.

Pour in the red wine. Use a wooden spoon to scrape the bottom of the pot thoroughly. Those browned bits are pure flavor. Let the wine simmer for 3 to 5 minutes to reduce slightly and concentrate the taste.

Return the browned beef to the pot. Add the bay leaf. Pour in enough water or beef broth to almost cover the meat. Bring the liquid to a gentle boil. Then, reduce the heat to low, cover the pot, and let it simmer. The stew needs approximately 2 to 3 hours. Stir occasionally and check the liquid level. Add a little more broth if the pot looks dry. The stew is ready when the beef falls apart easily with a fork and the sauce is rich.

About 30 minutes before the stew is done, start the potatoes. Peel the potatoes and cut them into evenly sized pieces. Place them in a pot of cold salted water. Bring to a boil and cook for 15 to 20 minutes, or until fork-tender. Drain them well in a colander.

Return the drained potatoes to the warm pot. Mash them with the butter and warm milk. Cold milk will cool the potatoes and make them gluey. Season with salt, black pepper, and a pinch of nutmeg. Mix until the potatoes are smooth and creamy.

Spoon a generous portion of creamy mashed potatoes onto each plate. Create a well in the center to hold the sauce. Top with the tender Beef Stew and plenty of the red wine sauce. Serve hot.