Dissolve bouillon cubes in water and bring to boil. Add celery, onions and broccoli, reduce heat and simmer until vegetables are tender, not mushy. Mix milk and cornstarch, a little at a time, and stir until all cornstarch is dissolved. Gradually add milk mixture to soup and stir constantly. Then add cheese cubes, stirring only until cheese is melted. Do not boil, as soup may curdle.