Heat oil in a large pot. Sprinkle lamb with flour, salt and pepper and cook half the lamb on both sides until brown. Repeat with the second half.
Remove the lamb from the pot. Add chopped bacon and cook to brown the meat and render the fat. This will be the foundation of our roux to thicken the stew.
Remove the bacon. Whisk in flour to make the roux. Continue to cook until it turns a light brown like so.
Stir in the onions, carrots and tomato paste. Cook until the onions soften, about four to five minutes. Add the garlic and cook for 30 seconds, stirring constantly.
Pour in the Guinness, scraping at the brown bits on the bottom of the pot to loosen. Now pour in the beef stock.
Add the lamb and bacon back to the pot. Tie the fresh herbs with kitchen twine and add those, the bay leaves and salt as well. Bring to a boil, cover and then reduce to a simmer.
After simmering, add potatoes to the pot and cook. Then, add the barley, bring to a boil and simmer again until the potatoes and barley are soft.
For a hearty Irish meal, make this Guinness lamb stew. You'll just love that flavorful, herby beer-spiked broth full of tender bites of lamb.