Season steak with 1 teaspoon salt and 1/2 teaspoon pepper.
Heat olive oil in a large stockpot or Dutch oven over medium high heat. Working in batches, add steak to the stockpot and cook, stirring occasionally, until evenly browned, about 6-8 minutes; set aside.
Reduce heat to medium. Add onion, carrots and celery. Cook, stirring occasionally, until tender, about 3-4 minutes.
Add garlic and mushrooms, and cook, stirring occasionally, until tender and browned, about 3-4 minutes.
Whisk in flour and tomato paste until lightly browned, about 1 minute.
Stir in wine, scraping any browned bits from the bottom of the stockpot.
Stir in beef stock, thyme, bay leaves and steak. Bring to a boil; reduce heat and simmer until beef is very tender, about 30 minutes.
Stir in potato; simmer until potatoes are just tender and stew has thickened, about 20 minutes. Remove and discard thyme sprigs and bay leaves. Stir in parsley; season with salt and pepper, to taste.
Serve immediately.
Notes
Prep ahead of time. Save time by prepping and dicing the meat and vegetables ahead of time (minus the potatoes as they will brown if chopped too early).
Sear the meat. Browning the beef first is key here. That dark crust on the sirloin steak will create such richer, deeper flavors in your stew (plus, the browned bits at the bottom of the pot are all lovely bits here, adding so much flavor).
Choose a wine you will drink. A dry red wine (cabernet sauvignon, pinot noir or merlot) is great here – it does not have to be anything fancy or overpriced. Just something you don’t mind sipping on since you will have an open bottle.
Use good-quality stock. The better quality your stock, the better your beef stew. Many brands love to pack in the salt so always opt for unsalted or a lower-sodium variety.
Serve with crusty bread. Serve with all the homemade crusty bread for dipping, sopping and dunking!