This heirloom recipe is per the request of my brother. It's a very old, authentic German recipe. My original copy is written on a scrap of tattered paper and doesn't go into much detail, so some of this is just from memory. I've put a star next to the memory parts. This recipe makes a huge amount. You may want to cut the ingredient amounts in half, especially on your first attempt. It is served warm or at room temperature. You may be shocked by the addition of bacon grease, but in the old, old days, the German people wasted nothing. Don't knock it until you try it. It's pretty darn good!
In large skillet, fry bacon over medium heat until crisp; transfer to paper towel; reserve grease; crumble bacon; set aside.
Wash unpeeled potatoes; place in extra large pot; cover with water by 1-2 inches.
Place pot on high heat; bring to boil; reduce heat to medium/medium-high. (* While potatoes are boiling, make the vinegar & sugar mixture. See step #6.)
Cook potatoes until barely fork tender (about 15 -18 minutes); remove from heat; drain, rinse with cool water for a minute to stop cooking process; drain.
When cool enough to handle, peel potatoes and *cut into slices about 1/3 inch to 1/2 inch thick (* I don't know why you couldn't just cut the potatoes into chunks as for any other potato salad) into large bowl.
For vinegar mixture: combine 1/2 cup vinegar with sugar, salt and pepper to your taste (* adding sugar, salt & pepper a little at a time until you get it how you like it ("till it suits you," as the old recipe states,) tangy yet sweet, with some saltiness and not too much pepper.)
Pour vinegar mixture over warm, sliced potatoes.
Add chopped onion and crumbled bacon to potatoes in bowl.
Warm up the reserved bacon grease (* not too hot, just warm enough to pour easily;) pour warm grease over potatoes; gently mix into potatoes and vinegar in bowl. (* I used 1/2 of the grease.)
Add "a big tablespoon" of mayonnaise (* to taste); gently incorporate into potatoes.
Taste and adjust mayo and seasonings to your liking.
Serve warm or at room temperature.
May be reheated in microwave at low power. (*Not in original recipe, lol!)
Cover and refrigerate leftovers.