First, preheat the oven to 400.
Line a large baking sheet with non-stick foil, and spray it with cooking spray.
Wash and dry the potatoes, and using a mandolin or a sharp knife, cut them into very thin slices (about 1/4” each).
Place the potato slices in a bowl, and toss with the olive oil and melted butter. Sprinkle with salt and pepper.
Arrange the potato slices not touching on the sheet pan, and roast for 10 minutes.
Flip the potatoes, and roast for another 10 minutes, or until golden brown and starting to turn crispy. )An additional 5-8 minutes may be necessary if you don’t have a super hot gas oven like me!)
Remove the potatoes from the sheet pan, and let them cool on a wire rack (this helps them crisp up).
Meanwhile, wrap the bacon in a few layers of paper towels, place on a plate, and microwave for 1 minute.
Flip the bacon and microwave another 30 seconds, or until almost crispy (it will crisp as it cools).
Crumble the bacon and set aside.
To assemble: layer the potato slices on one large plate (if sharing) or two smaller plates.
Top with grated cheese and bacon.
Microwave for just a few seconds to start melting the cheese.
Top with yogurt and scallions (if using), and then serve immediately.