Wrap the potatoes in aluminum foil and bake until soft, about 1 hour. Allow the potatoes to cool until they are cool enough to handle. When they are cool enough to handle, break them up into bite-sized pieces and set them aside.
Meanwhile, heat a large non-stick skillet over medium heat and cook the bacon until crispy. Once crispy, use a slotted spoon to transfer the bacon to a paper towel-lined plate. Drain and reserve the bacon fat from the skillet.
In a large bowl, combine the two kinds of cheese until well combined.
Working in batches, heat 1 tablespoon of the bacon fat in the skillet. Add a tortilla and top with roughly 2-3 tablespoons of the cheese mixture. Top with one-fifth of the potato pieces, bacon, and scallions. Season with salt and black pepper, then top with 2-3 more tablespoons of the cheese mixture, then top with another tortilla. Cook for 2 minutes, or until golden, then carefully flip the quesadilla over and cook another 1 to 2 minutes until the other side is golden and the cheese has melted.
Transfer the quesadilla to a cutting board and slice it into 6 pieces.
Repeat assembling and cooking the remaining ingredients to make quesadillas.
Serve with sour cream.
Notes
Store cooked quesadillas in an airtight container in the refrigerator for up to 3 days. Reheat them in a skillet over medium heat to restore crispiness or in the oven at 350°F for 10-15 minutes.
To freeze the quesadillas: Assemble the quesadillas and freeze them uncooked in a single layer. Once frozen, transfer them to a freezer-safe bag. Cook from frozen in a skillet over medium-low heat, adding a few extra minutes to ensure the potatoes heat through.