For the bacon mayonnaise:
Heat the oven to 425°F and arrange the racks to divide the oven into thirds.
Arrange the bacon pieces in a single layer on 2 rimmed baking sheets. Bake for 10 minutes. Rotate the pans between the oven racks and continue baking until the bacon is crisped and brown, about 5 to 10 minutes more.
Transfer the bacon pieces to a large paper-towel-lined plate, placing additional paper towels between each layer of bacon. Carefully pour the bacon fat from the baking sheets into a heatproof measuring cup—you need 2/3 cup. (If you don’t have enough bacon fat, add vegetable oil as needed.) Discard any excess bacon fat. Let the measured bacon fat cool for 15 minutes.
Place the egg yolks, vinegar, and mustard in a medium bowl and whisk until combined. While whisking constantly, very slowly add the bacon fat or bacon fat–oil mixture in a thin stream until it’s completely incorporated and the mixture is thickened and creamy. Add the salt and pepper and whisk to combine; set aside.
Once made, the bacon mayonnaise should be refrigerated in an airtight container; it will last up to 4 days.
Increase the oven temperature to broil and keep a rack in the top third of the oven.
Halve, core, and cut the apple into 1/8-inch-thick slices. Place the slices in a medium bowl, drizzle with the vinegar, and toss to coat.
Place 6 of the bread slices in a single layer on a clean baking sheet. Toast in the oven, flipping once, until lightly browned, about 1 minute per side. Transfer to a work surface and repeat with the remaining bread slices.
Spread 1 tablespoon of the bacon mayonnaise on each bread slice. Equally divide all of the apple slices among 4 of the bread slices. Top the apples with ham, 1 slice cheese, and another slice of bread. Top with the reserved bacon slices and another slice cheese; finish with the remaining 4 slices of bread, mayonnaise-side down. Slice each sandwich into quarters and serve.
Recipe adapted from: www.chow.com | by Lisa Lavery