1. In a large Dutch oven, add bacon over medium-high heat and cook until rendered and golden brown, about 8 minutes. Using a slotted spoon, transfer the bacon to a plate. Season the beef with salt and pepper. Sear the beef, working in 2 batches and turning as needed, until golden brown, 8-10 minutes. Transfer the beef to the plate with the bacon.
2. Add the onion to the pot and cook until softened and caramelized, 4-5 minutes. Pour in the wine and stir, scraping up any fond that has developed on the bottom of the pot. Cook until reduced slightly, 2-3 minutes.
3. Add back the seared beef and rendered bacon with the stock, potatoes, carrots, mushrooms and thyme. Bring to a boil, then reduce the heat to a simmer. Cook, covered, until the beef is tender, 2 hours.
4. In a small bowl, whisk cornstarch with 3 tablespoons water until smooth, then stir into stew and simmer until thickened, about 5 minutes. Season with salt and pepper, then divide between bowls and serve with mashed potatoes.