I was always very intrigued by this. Vinegar pie? All I could think of was sour/bitter and...nothing else. But the results were very surprising and tasty!
It turns out that vinegar pie is one of many pioneer recipes that was normally made when there was no more fruit. All the dried fruit and preserves had been consumed and no new fruit had ripened on tress yet. I found it mentioned in the Little House On The Prairie series of books.
What's fun is to make it for guests and call it a "fruit pie" without being specific. Then when all is eaten, ask them what fruit was in the pie. You will get puzzled looks and good guesses. And then surprised looks when they find out there is no fruit in the pie at all!
The only issue I have with the pie is that it has no form. It's sort of flat and thin. I guess because there is no fruit, the pie doesn't look to have much substance. I'd like to try it again and double the recipe. I think that would help.
The recipe I used was pretty good. However, the way it was all put together wasn't the best. It's a simple recipe and I found the explanations a little overdone.