In a large pot, cover the halved potatoes with water and add two good pinches of salt. Heat over medium-high heat until boiling. Reduce heat and simmer for 20-25 minutes or until a fork inserted pierces the skin easily. Drain and allow to rest for about 10 minutes
Meanwhile, cook the diced bacon in a large skillet until crispy. Remove to a paper towel to drain. Reserve about 1 cup of the fat.
Heat ¼ cup of bacon fat in a skillet over medium heat. Add the onions and cook, stirring frequently for 5-10 minutes or until translucent. Set the onions aside with the bacon to drain.
For the dressing: In a large mixing bowl, combine the mustard and vinegar. Slowly whisk in the remaining ¾ cup bacon fat into the vinegar mixture. Add salt and pepper to taste.
To assemble: Add the drained potatoes to the vinaigrette, tossing to coat completely. Add the red onions and about ¾ of the bacon and allow to rest for 10-15 minutes.
Serve topped with remaining bacon and green onions. Enjoy!
Recipe by This Cookin' Dad at https://thiscookindad.com/2015/05/warm-german-potato-salad/