Combine all stock ingredients, bring to a boil & simmer for 30 minutes. Let stand till needed & then drain befroe using.
Heat oil in a soup pot. Add chopped leeks & saute over moderate heat, stirring frequently, til lthe leeks start to go limp. Add stock, turnips, celery & bay leaves. Bring to a boil, cover & simmer for 10 minutes. Add tomatoes (including their juice) & mushrooms, simmer another 15 to 20 minutes. Season to taste & remove from heat.
Allow soup to stand for several hours or cool & refrigerate overnight. Before serving, heat through, add parsley & dill. Top each serving with matzo farfel if desired.