*NOTE: When I was preparing this recipe for posting, I used red onion in place of yellow onion. The red onion turned the salad dressing a very pretty shade of pink! Substitute yellow onion if you wish.
In non-reactive bowl (or blender), combine the sugar, dry mustard, salt, celery seed, onion, and the optional lemon thyme.
If using a mixer, gradually pour the vinegar and oil into the bowl while the beaters are on. Keep beating until the salad dressing is smooth, scraping down the sides of the bowl if necessary.
If using a blender, cover the blender and slowly start pouring in the oil and vinegar through the opening on top of the blender cover. Keep the motor running while blending all the ingredients until mixed well. With spatula, scrape down the sides of the blender bowl.
Taste and adjust seasoning if necessary.
For best results, allow salad dressing to marinate for 1 hour.
Toss salad dressing with fruit salad just before serving.