Broth-based soups provide a starting point for a dish that can serve as either a starter or as a complete meal. Thickening the soup with a roux, which is a blend of flour and fat, adds body and substance to an otherwise watery base by providing a creamier texture and a richer flavor. You can use a roux at the start of your recipe or at the end to finish the soup if the stock is still not quite as thick as you'd like it. It takes about 2 tablespoons of flour and an equal amount of butter, oil or pan drippings to thicken 1 cup of stock.
Measure out 2 tablespoons of butter or oil for each cup of stock in the soup and place in the bottom of a stock pot or saucepan. Set the burner on medium heat and allow the butter to melt completely, or heat the oil until hot but not smoking.
Add finely chopped seasoning vegetables, such as onions, garlic and celery, and cook for 2 to 3 minutes or until just tender. Measure out an amount of flour that is equal to the amount of butter or oil in the saucepan and sprinkle it evenly across the sautéed seasoning vegetables.
Cook and stir the butter, flour and vegetable mixture for about two minutes to get rid of the raw flour taste, adding a little more butter or oil if the mixture appears too dry.
Slowly pour in the stock in small amounts, stirring constantly to prevent lumps from forming. Cook and stir until the stock starts to thicken, then add a little more stock. Continue doing this until you have used up all the stock, which can take up to 10 minutes.
Lower the heat to keep the thickened stock warm while you assemble other pre-cooked ingredients going into the soup, such as diced or shredded meats, cubed potatoes, sliced carrots, frozen green peas, egg noodles and white rice.
Add the seasonings, including salt and pepper, and adjust for flavor. Simmer the soup until all of the ingredients are heated through.