Fill 4-quart saucepan two-thirds with water; heat to boiling over high heat. Cook sliced potatoes in water 6 to 9 minutes or until almost tender; drain and return to saucepan.
Heat oven to 350°F. Spray 3-quart casserole with cooking spray.
In 12-inch nonstick skillet, melt 2 tablespoons butter over medium heat. Cook and stir leeks in butter about 5 minutes or until softened. Stir in flour. Gradually stir in half-and-half. Heat to boiling. Remove from heat. Stir in cheese, dill, salt and pepper until cheese is melted.
Pour sauce over potatoes in saucepan. Spoon half of potato mixture into casserole. Top with half the salmon. Repeat layers.
Stir together bread crumbs and melted butter; sprinkle over potato mixture. Bake uncovered 30 to 40 minutes or until potatoes are tender and topping is golden brown.