Use a mandolin to cut the potatoes in even and thin slices. Place them in a stock pot and cover the with cold salted water. Bring to a boil and cook until tender. Drain and transfer to a bowl. (Note: I used baby potatoes to get small slices).

While the potatoes are cooking, cook the bacon slices until crispy. Remove and drain on a paper towel. Crumble the bacon and set aside. Reserve bacon fat.

Note: You'll need 2 Tablespoons of fat. If the bacon drippings is less, add a little olive oil.

Heat up the 2 Tablespoons of bacon fat/olive oil in a medium skillet and saute the onion until softened - about 5 minutes. Remove from heat and set aside.

In a Pyrex measuring cup, whisk together the apple cider vinegar, Dijon mustard, salt and pepper. Combine with the onion and bacon fat. Add the scallions and toss with the warm potatoes to coat.

Add the crumbled bacon and fresh dill and toss to combine. Taste and reseason, if necessary. Serve immediately.