Pat the beef sirloin dry with paper towels and season evenly with sea salt and black pepper.
Heat the olive oil in a heavy-bottomed pot or Dutch oven over medium-high heat and sear the beef until a dark golden crust forms on all sides.
Remove the beef from the pot and set aside, then add the pearl onions, sliced carrots, and halved mushrooms to the same pot.
Sauté the vegetables for 5-7 minutes until they begin to soften and brown slightly.
Stir in the minced garlic and tomato paste, cooking for 1 minute until the paste turns a deep brick red.
Pour in the dry red wine to deglaze the pot, using a wooden spoon to scrape up all the flavorful browned bits from the bottom.
Return the beef to the pot and add the beef broth, fresh thyme, and the bay leaf.
Reduce the heat to low, cover with a tight-fitting lid, and simmer for 90 minutes or until the beef is fork-tender.
Remove the bay leaf and serve the stew hot in shallow bowls.