Basic formula seems to be:
1/3 cup jam (pretty much any flavor)
1/4 cup olive oil
1/4 cup vinegar
salt/pepper to taste
Whisk all ingredients together. Remove big clumps of fruit/seeds for best results. Voila.
Ordinarily in a vinaigrette you want less vinegar than oil. But in this one you might want equal amounts, or even more vinegar than oil, to counteract the excessive sweetness of the jam. Taste as you go; you'll get it right. Tried it tonight with blackcurrant jam. Much better than expected. A trick to be used again.
* I realize the answer could quite possibly be, "Yes, I already knew that. What are you, stupid? Been living under a rock where they don't get culinary news?" Getting lambasted for sharing new things you learned is part of the joy of posting on the internet. On the other hand, there may be some people - intelligent people, even; good people - for whom the answer is, "Why, no, I never tried that." And maybe those people need vinaigrette, and have extra jam, and also happen to love household tips. So for you, my Ideal Reader, I submit this tidbit.
How the Amazon.com ratings would go if this were a product they sold:
FIVE STARS from MaryJo in Kennewick - Love it!!! Best salad dressing ever, and soooo easy! Try it; you won't regret it!
ONE STAR from KeriAnn in Gresham - Ick!! Grossest thing I ever tasted!!! DON'T WASTE YOUR TIME!!!!! Why don't they let us give ZERO stars???!!!
(Yes, I spent some time today trying to compile a registry on Amazon, and got quite exasperated with the contradictory user reviews for every single imaginable product. Who can you trust? MaryJo, or KeriAnn, or who, I ask you?)