Preheat oven to 350°F. Cook the macaroni according to package directions, drain well, and set aside.

In a large bowl, stir the warm macaroni with sour cream until every noodle is coated. Fold in the crab meat gently.

Finely chop the spring onion and set aside.

Melt butter in a saucepan and add the shrimp; sauté until they just turn opaque. Remove shrimp, roughly chop, and add to the macaroni.

In the same pan, sauté the spring onion until tender. Sprinkle the flour over the onions and stir for about one minute.

Slowly whisk in the evaporated milk and stir until the sauce thickens. Gradually add grated cheddar, stirring until smooth.

Pour cheese sauce over the macaroni and seafood and fold to combine. Taste, then add salt and black pepper.

Transfer mixture to a buttered baking dish. Sprinkle with grated mozzarella, panko crumbs, and a light dusting of paprika.

Bake for 20-25 minutes until the top is lightly browned and bubbling; let rest for 5 minutes before serving.