Place sliced potatoes in a large pot, cover with water, and bring to a boil.
Cook for 10-12 minutes until just tender (do not overcook). Drain and set aside.
In a skillet over medium heat, cook chopped bacon until crispy.
Remove bacon with a slotted spoon, leaving 2 tbsp bacon fat in the pan.
Add diced onion to the bacon fat and cook until softened (~3 minutes).
Stir in flour, sugar, salt, and pepper. Cook for 1 minute.
Whisk in mustard, vinegar, and water/broth. Simmer until thickened (~3-5 minutes).
Gently fold cooked potatoes and bacon into the warm dressing.
Garnish with fresh parsley.
Serve warm or at room temperature.
