In large saucepan, melt butter. Add celery and onions and cook until tender.
Add water, cabbage and carrots and bring to a boil. Cover and let simmer, stirring
occasionally until cabbage and carrots are tender.
Add chicken noodle soup mix.
Blend together dry mustard and flour with milk to make a paste; stir this mixture
into the saucepan and bring to a boil. Simmer, stirring constantly, until thickened,
about 5 to 10 minutes.
Add corned beef and stir until heated through, being careful that it doesn't
stick to the bottom.