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1
Heat the oven to 425 degrees F and arrange the racks to divide the oven into thirds.
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2
Arrange the bacon pieces in a single layer on 2 rimmed baking sheets.
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3
Bake for 10 minutes.
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4
Rotate the pans between the oven racks and continue baking until the bacon is crisped and brown, about 5 to 10 minutes more.
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5
Transfer the bacon pieces to a large paper-towel-lined plate, placing additional paper towels between each layer of bacon.
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6
Carefully pour the bacon fat from the baking sheets into a heatproof measuring cupyou need 2/3 cup.
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7
(If you dont have enough bacon fat, add vegetable oil as needed.)
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8
Discard any excess bacon fat.
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9
Let the measured bacon fat cool for 15 minutes.
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10
Place the egg yolks, vinegar, and mustard in a medium bowl and whisk until combined.
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11
While whisking constantly, very slowly add the bacon fat or bacon fatoil mixture in a thin stream until its completely incorporated and the mixture is thickened and creamy.
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12
Add the salt and pepper and whisk to combine; set aside.
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13
Increase the oven temperature to broil and keep a rack in the top third of the oven.
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14
Halve, core, and cut the apple into 1/8-inch-thick slices.
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15
Place the slices in a medium bowl, drizzle with the vinegar, and toss to coat.
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16
Place 6 of the bread slices in a single layer on a clean baking sheet.
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17
Toast in the oven, flipping once, until lightly browned, about 1 minute per side.
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18
Transfer to a work surface and repeat with the remaining bread slices.
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19
Spread 1 tablespoon of the bacon mayonnaise on each bread slice.
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20
Equally divide all of the apple slices among 4 of the bread slices.
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21
Top the apples with the ham and another slice of bread.
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22
Top with the reserved bacon slices and finish with the remaining 4 slices of bread, mayonnaise-side down.
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23
Slice each sandwich into quarters and serve.
