Bring a pot of water to a boil and add the sliced red potatoes, cooking until tender, about 15 minutes. Visual cue: the slices should pierce easily with a fork.

Drain the potatoes and keep them warm while you cook the bacon and dressing. Visual cue: steam should still rise from the drained potatoes.

Cook the bacon in a skillet over medium heat until crispy, about 10 minutes, then drain and crumble, and set aside. Visual cue: bacon pieces should be browned with a crisp edge.

Reserve 3 tablespoons of bacon drippings in the skillet. Visual cue: you should have a thin, shimmering layer of fat.

Sauté the diced onion in the reserved bacon drippings until soft, about 5 minutes. Visual cue: onion pieces should turn translucent and glossy.

Add the apple cider vinegar, sugar, Dijon mustard, and chicken broth to the skillet, then bring to a simmer. Visual cue: small bubbles should form around the edges and the sauce should look slightly thickened.

Pour the hot dressing over the warm potatoes. Visual cue: the potatoes should start looking glossy and coated right away.

Add the crumbled bacon and chopped fresh parsley, then toss gently to combine. Visual cue: parsley should be evenly scattered without breaking the potato slices.

Serve the German potato salad warm. Visual cue: bacon-vinegar dressing should look shiny at the bottom of the bowl.