3/4 cup all-purpose flour, seasoned with (preferably kosher, coarse) salt and freshly ground black pepper, for coating
How to make it
Place each cutlet between two sheets of waxed paper and pound with a meat pounder or rolling pin until very thin. Place the cutlets as they are pounded in a shallow dish with milk to cover (use a little more or less milk than listed, as necessary) while you assemble the remaining ingredients for the sandwiches.
Open the buns and toast them. Then lay them out on your work surface. Spread 1 tablespoon mayonnaise and 1 teaspoon mustard on the top half of each bun, then press 2 pickle slices gently into the spread on each top. Divide the lettuce among all the bun bottoms, topping each with a slice of tomato and onion.
Heat the oil in a large skillet over medium-high heat. While it heats, spread flour on a plate and dip half the pork pieces, one by one, in the flour (use a little more or less flour than listed, if necessary) to coat completely, shaking off any excess. Place the cutlets in the hot oil, arranging them so they don't touch and fry until crispy and golden, about 1 minute per side. Using a slotted spatula, transfer the cutlets to paper towels while you coat and fry the remainder.
Place 2 fried pork cutlets on the bottom half of each bun, replace the tops and serve immediately.