Saute the kielbasa until golden brown on all sides in a large, hot soup pot, about 4 minutes per side. The sausage will not be cooked through, It will finish cooking in the soup. Remove from the pan and set aside.
In a large pot, heat the oil over medium-high heat. Add the onions, salt, pepper and bay leaves, and cook, stirring, until the onions are slightly caramelized, 12 to 15 minutes. Add the garlic and cook, stirring, until fragrant, about 1 minute. Sprinkle the flour over the onions and cook, stirring constantly, for 2 minutes. Gradually whisk in the stock and beer. Add the thyme and bring to a boil. Reduce the heat to medium-low and simmer uncovered, stirring occasionally, for 1 hour.
During the last 15 minutes of cooking, add the kielbasa and cook until sausages are cooked through. Remove the cooked sausages from the soup. Add the cheese 1/3 cup at a time, stirring until nearly all melted and smooth after each addition. Remove from the heat and adjust the seasoning, to taste. Ladle into 1 or more thermoses.
Place sausages in each thermos. The hot soup will keep the sausage warm until you are ready to eat it. Pack a roll for the sausage as well. When it's time to eat the soup, remove the kielbasa and place it on the roll - soup and a sandwich on the go! Garnish with parsley, garlic croutons, and finely grated cheese.
Yield: 6 to 8 servings