Preheat the oven to 350°F and boil salted water for the macaroni.

Cook pasta al dente per package, then drain well and return to a large bowl.

Stir in the sour cream until every noodle glows with creaminess, then fold in the claw crab meat gently.

Melt butter in a skillet over medium heat and add the shrimp; cook until just opaque, about 2–3 minutes per side.

Remove the shrimp, let cool briefly, chop slightly, and add to the macaroni.

Finely chop the spring onion and sauté the white parts in the same pan until tender and fragrant.

Sprinkle the flour over the onions, stir, and let it toast for about one minute.

Slowly pour in the evaporated milk while whisking until the sauce thickens and coats the back of a spoon.

Gradually stir in the grated cheddar until smooth and silky.

Pour the hot cheese sauce over the macaroni and seafood, season with salt and black pepper, and stir until combined.

Transfer the mixture to a well-buttered baking dish, top with shredded mozzarella and panko, and dust lightly with paprika.

Bake for 20–25 minutes until golden and bubbling at the edges.

Let rest a few minutes before serving.