Make the pork: Cut the tenderloin into quarters; using a meat mallet, pound each piece until it is 1/4 inch thick and about 6 inches wide. Mix the buttermilk and barbecue rub in a baking dish, add the pork, cover and let marinate overnight or up to 2 days.
In a large deep saucepan, heat the peanut oil over medium heat until a deep-fry thermometer registers 350 degrees F. Take the pork out of the marinade and season with salt and pepper.
Make a three-stage breading station with the flour, eggs and crouton crumbs in separate shallow bowls. Place the pork pieces first in the flour, turning to coat; shake off the excess. Dip the pork in the beaten egg and let the excess drip off, then dredge in the crouton crumbs, pressing until total coverage is achieved.
Fry the pork in batches until golden brown, 4 to 5 minutes. Let drain on a paper towel?lined baking sheet. Set aside.
Make the aioli: Mix the mayonnaise, habanero sauce and granulated garlic in a small bowl. Season with salt.
Build the sandwiches: Place the crispy pork on the toasted buns with some pickle slices, shredded lettuce and then a nice schmear of the aioli. Serve with extra aioli on the side.
Photograph by Steve Giralt