Preheat the oven to 425°. Place 6 slices of the bacon on each of two baking sheet pans. Cook until bacon is crisp, about 10-12 minutes. Transfer bacon to a plate lined with paper towel to cool and drain. Chop when cool enough to handle.
Divide the potatoes evenly onto the two baking sheet pans and toss in the rendered bacon fat. Spread on the pans in a single layer to make room between the wedges. (The potatoes don’t brown when crowded). Roast, rotating the pans about halfway through cooking, for about 35 minutes, until lightly browned and tender in the center.
While the potatoes cook, make the dressing: whisk together the Dijon, salt, vinegar and olive oil. Toss the warm potatoes with the dressing and allow them to stand, stirring occasionally, until slightly warm but not hot, about 15 minutes.
Stir in the bacon, scallions and cheese. Serve warm or at room temperature.
* Larger potatoes may be used and cut in ½-inch thick wedges.