Prepare potatoes, carrots, and onions. Place in large
pot and add salt and water. Cook until vegetables are
tender, about 20 minutes. Add broccoli, chicken base,
and milk. Simmer for 5 more minutes. In separate pan,
melt margarine and add flour and dry mustard; stir to
make roux mixture. Add to soup and stir until
thickened. Add cheese to soup. Stir till cheese is
melted. Keep hot, but do not boil, until ready to serve.