Sauté until the onions are tender, then add a bottle of Guinness®. Scrape the browned bits from the pan while stirring. Add the tomato paste and stir well to mix it in with the beer.
Add the carrots, thyme, and the remaining half bottle of Guinness.Stir gently until the liquid is an even consistency, and leave to simmer for 2 to 3 hours.