Heat oil or butter in a large pot over medium-high heat. Season beef with salt and pepper. Sear until deeply browned on all sides. Remove beef and set aside.
Add mushrooms to the pot. Cook until browned. Add onions, garlic, tomato paste, and thyme. Stir constantly for 1 minute.
Pour in Worcestershire sauce and a splash of broth. Scrape up the browned bits from the bottom of the pot.
Return beef to the pot. Add potatoes and the rest of the broth. Bring to a boil, cover, and lower heat to a gentle simmer. Cook for 50-60 minutes until beef is tender.