Mix Sugar, Mustard, Salt and Vinegar.
Add Onion juice and stir thoroughly.
Slowly add Oil, beating constantly and continue to beat until thick.
When you think the mixture is thick enough, beat 5 minutes longer.
Add Poppy Seeds and beat for a few minutes.
Store in a cool place or in the refrigerator.
If the dressing separates, pour off the clear part and beat again; add the Poppy Seed mixture slowly, but it will not separate unless it becomes too cold or too hot.