Wash and chop each leg quarter into thirds.
Marinate the chicken with fish sauce, garlic salt, black pepper, chopped garlic and shallots. Cover and refrigerate for a few hours. Before cooking the chicken be sure to bring the chicken back to room temperature.
Wash and cut the carrots, tomatoes and potatoes. Slice the mushrooms if they have not been pre-sliced. Cut the onion into wedges. Mince the garlic. Set aside.
Wash, peel and cut the potatoes into cubes. Fill a bowl with some water and add a tablespoon of salt. Place the cut potatoes into the bowl of salted water to keep them from turning brown. Leave the potatoes in the salted water until you are ready to add them to the soup. Before adding the potatoes to the soup be sure to give the potatoes a quick rinse. Set aside.
Saute the tomatoes. In a saute pan on Medium High heat add 2 tablespoons of vegetable oil. Once the oil is warm add 1 tablespoon of garlic. Saute for 30 seconds. Then reduce the heat to Medium and add in the tomatoes. Saute for about 2-3 minutes. Add in 1 tablespoon of sugar and 1 teaspoon of salt. Cook the tomatoes until slightly softened. Set aside.
Cook the chicken. In a wok on Medium High add 1/4 cup of vegetable oil. Once the oil is warm add in 1 tablespoon of garlic and saute for 30 seconds. Then add in the chicken and let them sit in the pan for about 2-3 minutes undisturbed. Then saute the chicken until it is halfway cooked. Set aside.
Make the sauce. In a large pot on High heat add 2 tablespoons of vegetable oil plus 1/2 stick of butter. Once the butter is melted reduce the heat to Medium then add in the tomato paste. Stir. Saute for another minute then add in the Prego Sauce and stir. Add in the Chicken Broth and stir. Add 1 tablespoon of sugar and 2 tablespoons of salt. Add the Bay leaves. Add in the tomatoes and stir. Bring the sauce to a boil.
Then add in the chicken . Discard the fat and juices at the bottom of the wok.
Also add in the carrots and potatoes. Bring the sauce back to a boil once more.
Cover and simmer for 15 minutes. Stir occasionally.
Add the mushrooms and sliced onions . Bring the ragu back to a boil. Then cover and simmer for another 20 to 30 minutes until the chicken is cooked through and the vegetables are slightly softened. Stir occasionally.
Taste and adjust the soup. If you want it sweeter add more sugar. If it is too thick or salty add some water. If it needs more flavor you can add some chicken seasoning.
Turn off the heat and leave the pot on the stove with the lid slightly uncovered for 30 minutes. This will allow the chicken to become tender.
Ladle into a bowl. Sprinkle on some black pepper and garnish with Thai Basils.
Serve with french bread.