Melt butter in saucepan. Add chopped onion and cook just until the onion is transparent. Add flour and blend over low heat. Stir in milk slowly to make cream sauce base. Cook and stir until the sauce is thick, then gradually add the chicken broth. In a blender, puree the stewed tomatoes and then add to cream sauce mixture. Stir in fresh dill and grated cheese or cheese may be sprinkled on top just before serving. Garnish with fresh dill.