To prepare the shoestring onions, in a large bowl, whisk together the buttermilk, hot sauce and egg. Add the onions and refrigerate for 30 minutes.

Remove the onions from the refrigerator. Fill a large pot or deep fryer one-third full with vegetable oil and heat to 350°F. 

In a clean brown paper bag, combine the flour, cornmeal, 1 tablespoon of the garlic salt and 1/4 teaspoon of the cayenne pepper. Drain the onion rings and add them to the paper bag. Shake the bag until the onions are covered with the flour mixture, then let sit for 5 minutes.

Gently add half of the onions to the hot oil and fry them, uncovered, until golden brown, about 4 minutes. Transfer the onions to paper towels to drain, and season them with 1/2 tablespoon of the remaining garlic salt and 1/8 teaspoon of the cayenne. Then fry, drain and season the second batch with the remaining 1/2 tablespoon garlic salt and 1/8 teaspoon cayenne.  

Meanwhile, prepare the slider filling: In a large sauté pan over medium heat, warm the olive oil. Add the onion, bell pepper, jalapeño and chipotle peppers and cook, stirring occasionally, until soft.

Add the ground beef and garlic, breaking up the meat with a wooden spoon, and cook until the meat is browned. Add the tomato sauce, tomato paste, vinegar, wine, Worcestershire, brown sugar, paprika, salt, black pepper, cayenne pepper, cumin and mustard. Reduce the heat to low, cover and simmer the sauce for 30 minutes.
  
To serve, spoon the meat sauce onto the bottom half of each toasted bun, top with a haystack of fried onions and cover with the top bun.