In a 4 quart casserole dish combine cubed potatoes, carrots, celery, onion, water and salt. Microwave on high for 15 minutes or until vegetables are crisp tender.
Stir in broccoli, bouillon cubes, margarine, dry mustard, pepper, and processed cheese. Set aside.
In a small bowl combine the milk and flour and blend until smooth. Slowly add to cheese mixture, stirring until blended. Microwave on medium-high (70 percent) for 20 minutes, or until temperature reaches 160 degrees.