Melt the butter in the skillet. Add the carrots, garlic, potato and onion and cook until lightly colored, about 3 minutes. Stir in the flour. Add the red wine and simmer, scraping up any browned bits from the bottom of the pan. Add the stock, thyme sprigs and bay leaf and bring to a boil. Cover and simmer over moderately low heat until the carrots and potato are fork tender, about 6 minutes.