Amish Slaw

1 cup vinegar
1/2 cup vegetable oil
1/4 cup water
1 teaspoon mustard
1 teaspoon celery seed
1 teaspoon sugar
1 1/2 teaspoons salt
1 medium cabbage
2 medium onions
1 cup granulated sugar

Mix vinegar, oil, water, mustard, celery seed, sugar and salt; boil for 3 minutes. Mix cabbage, onions and sugar. Combine boiled mixture and cabbage mixture; refrigerate overnight.