Pre-heat oven to 400 degrees. Place bacon slices in a single layer on a cooling rack placed inside a baking sheet. If you don't have a cooling rack, simply line the baking sheet with foil before placing bacon on top. Bake until bacon is crispy, around 15 minutes.
While bacon is baking, cook the potatoes by placing them in a pan then covering with cold water. Boil until fork tender, about 12-15 minutes. Strain and set aside.
Follow this tutorial to hard boil the eggs to your desired doneness. Let eggs cool enough to peel then chop into bite-sized pieces. Place cooked potatoes in a large bowl along with diced, cooked eggs.
Remove bacon from oven and chop into small pieces. Add to the bowl along with the potatoes and eggs.
In a medium bowl, whisk together dressing: mayo, vinegar, mustard, sugar, salt and pepper. Drizzle dressing over the potatoes, bacon and eggs then toss to coat. Sprinkle in scallions before serving. Can be served warm, room temperature or chilled.