Season the beef with salt and pepper and dust with 2 tablespoons flour.
Heat 3 tablespoons oil in a large skillet over medium-high heat. Just before the skillet is smoking hot, add the beef, in batches, and cook until well browned, about 8 minutes.
Remove meat directly to slow cooker and repeat with the second batch. (Be careful not to overcrowd your pan or the beef
will not brown.)
Once all the beef has been browned, lower the heat to medium, add the remaining tablespoon oil, and stir in the tomato paste.
Sprinkle in the remaining flour and stir until thick and pasty.
Slowly whisk in the stout and broth and scrape up any browned bits from the bottom of the pan.
Once thickened and steaming, add sauce directly to the slow cooker.
Stir in carrots, potatoes, onion, thyme, and add a big pinch of salt and pepper.
Cover slow cooker with lid and cook for 4 to 5 hours on high, or 8 to 9 hours
Serve in bowls with a dollop of horseradish, if desired .
Tip: We use chicken broth in this stew as we find beef stock can become salty and strongly flavored in a long-cooking stew.