From Granny Ethel Vera Jack Hoffman
1 cup prepared mustard
1 cup sugar
3 TBSP flour
3 TBSP butter
1/4 cup vinegar
1 can crushed pineapple, drain and reserve liquid
1/2 tsp salt
Melt butter in sauce pan. Remove from heat. Add flour and stir. Add sugar to flour mixture and stir. To reserved liquid from crushed pineapple, add enough water to make 1 cup of liquid. Slowly add the liquid to the flour mixture, stirring to prevent lumps. Add remaining ingredients, then heat to boiling over medium heat while stirring frequently.
This makes a lot of sauce, I usually freeze half of it to use later.