Recipe(tried): Warm German Potato Salad

It's vinegar, although, it depends on who you talk to...my grandmother, who's family is "off the boat" German, made it like this. And I apologize for the lack of proper measurements as this was told me by my grandmother...

Warm German Potato Salad

Red or Yukon Gold Potatoes (matter of preference)
A pound of a good quality bacon
Sweet Vidalia Onions
Vinegar, preferably cider
Water
Salt and Pepper to taste

Boil your potatoes until, tender but still firm.
Slice and let cool.
Cut the bacon into small pieces. Cook until crisp with sliced onion. When onions soft add vinegar and salt and pepper. Let simmer, add small amounts of water and vinegar until you get desired taste. Toss sauce with potatoes and serve warm. You can also keep warm in the oven, that's what my grandmother used to do, not too long though because it can and will get mushy.

Some people add sugar to kill the bitterness of the vinegar...again, preference...

Hope this helps!