Soak the salt cod in plenty of cold water for 12 to 24 hours, changing the water several times, until it is no longer salty. Drain and flake into small pieces.

Put the salt cod into a saucepan with the milk, the water, and the bay leaf (bouquet garni). Bring to a gentle simmer and cook for 15 minutes. Remove from the heat and let stand briefly.

Add the fresh cod fillets to the pan and cook about 5 minutes more, just until the fresh cod is done. Do not overcook. Drain both cods well, reserving no liquid.

In a large bowl combine the drained cod with the green onions, the minced jalapeño, the eggs, half of the bread crumbs, the cornmeal, and the flour. Season the cod mixture with salt and pepper to taste. The mixture should hold together; if it is too wet, add a little more bread crumbs.

Turn the mixture onto a work surface and form it into 6 to 8 patties about 1/2 inch thick. Coat the patties evenly with the remaining bread crumbs.

Heat the oil in a large skillet over medium heat until hot but not smoking. Fry the cakes, turning once, until golden and crisp on both sides, about 3 to 4 minutes per side. Drain on paper towels.

For the tartar sauce: combine the mayonnaise, capers, lemon juice, salt, and pepper. Chill until serving.

Serve the hot cod cakes immediately with the jalapeño tartar sauce.