Combine the buttermilk, salt and pepper in a shallow bowl. On a large plate, toss together the panko bread crumbs and Old Bay seasoning.
In a large heavy-bottom pot or Dutch oven, heat 2 inches of oil until a deep-fry thermometer reads 350°F. One at a time, dip a piece of fish in the buttermilk, shake off any excess and dredge in the panko mixture.
Gently place the fish pieces in the oil being careful not to overcrowd the pot. Fry for 2 minutes on each side or until golden brown. Use tongs to transfer the fish to a wire rack placed over a baking sheet and season with a sprinkling of kosher salt while the fish is still hot.
While the fish is cooking, toast the buns.
To assemble the sandwiches, spread the tartar sauce on the bun and top with the fried shad and your choice of extras.
