1. In a large Dutch oven or heavy-bottomed pot, heat the tallow over medium-high heat. Add the beef cubes in a single layer and brown on all sides, about 3-4 minutes per side. Work in batches if needed to avoid overcrowding the pot.

2. Remove the browned beef and set aside. Add the diced onion to the pot and cook for 5 minutes, stirring occasionally, until softened.

3. Add the minced garlic and cook for 1 minute, until fragrant.

4. Pour in the Guinness beer and use a wooden spoon to scrape up any browned bits from the bottom of the pot.

5. Add the browned beef back to the pot, along with the beef broth, carrots, potatoes, bay leaves, and thyme. Season with salt and pepper.

6. Bring the stew to a boil, then reduce heat to low, cover, and simmer for 45-60 minutes, until the beef is very tender and the vegetables are cooked through.

7. Remove the bay leaves and thyme sprigs. Taste and adjust seasoning as needed.

8. Serve the Guinness & Tallow Beef Stew hot, with crusty bread on the side.