Aunt Karen's Famous Poppy Seed Dressing

This is a favorite salad dressing at our house. I have had many requests for the recipe although, I can't take the credit for it since this recipe was given to me by my aunt:)
I hope you enjoy! ~Grace

1-1/2 Cups Granulated Sugar
1 tsp. Dry Mustard
2 tsp. Salt
1/2 Med. Onion
2/3 Cup Cider Vinegar
2 Cups Vegetable Oil
2 tsp. Poppy Seeds

Chop onion and vinegar in blender. Add sugar, dry mustard, salt and blend. Add oil 1/4 cup at a time, blend well each time. Stir in poppy seeds with spoon. Refrigerate.

Note: dressing will separate if not blended long enough after each oil addition.