Using paper towels, pat fish dry; season with Old Bay seasoning, salt and pepper, to taste.
Working one at a time, dredge fish in flour, dip into the buttermilk mixture, then dredge in Panko, pressing to coat.
Heat vegetable oil in a large stockpot or Dutch oven over medium high heat until it registers 360 degrees F on a deep-fry thermometer.
Working in batches, add fish and fry until golden brown, turning occasionally, about 3-4 minutes. Transfer to a baking sheet fitted with a wire rack and keep warm.*
To serve, spread buns with tartar sauce, then top with fish and cheese slices.
for the buttermilk mixture
In a medium bowl, whisk together buttermilk, egg and hot sauce.
for the homemade tartar sauce
In a small bowl, whisk together mayonnaise, relish, dill and lemon juice; season with salt and pepper, to taste.
Notes
*Panko is a Japanese-style breadcrumb and can be found in the Asian section of your local grocery store.*The fish can be kept warm, up to 30 minutes, in the oven at 200 degrees F.