01 - Arrange cod fillets in a shallow saucepan with the bay leaf, milk, and enough water to cover. Bring just to a simmer and poach until opaque and easily flaked, about 5 to 7 minutes. Remove cod from liquid, drain thoroughly, and flake into a large mixing bowl. Discard bay leaf and poaching liquid.
02 - In a separate pot, boil diced potatoes in salted water until fork-tender, approximately 12 to 15 minutes. Drain well, then mash until smooth and let cool slightly.
03 - To the flaked cod, add mashed potatoes, minced shallot, chopped parsley, Dijon mustard, beaten egg, panko breadcrumbs, salt, and pepper. Gently mix until just combined without overworking the mixture.
04 - Divide mixture into 8 uniform portions and shape into patties. Arrange on a tray, cover, and refrigerate for at least 20 minutes to firm.
05 - Spread extra panko on a plate. Gently coat each patty in breadcrumbs, pressing to adhere on both sides. Heat vegetable oil in a large skillet over medium heat. Fry cod cakes in batches for 3 to 4 minutes per side until golden brown and crisp. Drain on paper towels.
06 - In a small bowl, combine mayonnaise, lemon juice, chopped pickles, dill, capers, Dijon mustard, lemon zest, a pinch of salt, and freshly ground black pepper. Mix thoroughly and refrigerate until ready to serve.
07 - Arrange crispy cod cakes on a platter and serve warm with lemon-dill tartar sauce on the side.