Butter an 8 x 8 x 2-inch glass baking dish.

Melt unsalted butter in a heavy large saucepan over medium heat.

Add thinly sliced leeks and celery seeds to the saucepan.

Sprinkle lightly with coarse kosher salt.

Cover saucepan and cook until leeks are tender but not brown, stirring often, about 8 minutes.

Add all-purpose flour; stir 1 minute.

Gradually add whole milk and half and half; simmer until the mixture thickens slightly, stirring often, about 5 minutes.

Stir in fresh lemon juice.

Season leek sauce to taste with coarse kosher salt and pepper.

Remove sauce from heat.

Meanwhile, cook wide egg noodles in a large pot of boiling salted water until tender, stirring occasionally.

Drain noodles, reserving 3/4 cup noodle cooking liquid.

Transfer noodles to a large bowl.

Pour leek sauce over noodles.

Add grated Gruyere cheese and chopped fresh dill and stir to blend.

Add reserved noodle cooking liquid by tablespoons until mixture is moist and creamy (about 8 tablespoons).

Fold in drained and broken albacore tuna.

Transfer to prepared baking dish.

Preheat oven to 375°F.

Bake noodle casserole, covered with foil, until heated through, about 20 minutes if freshly made or 30 minutes if chilled.

Remove foil.

Sprinkle coarsely crushed salted potato chips over and continue to bake, uncovered, until top is golden brown and filling bubbles, about 10 minutes longer.

Serve hot.