Boil the lasagna noodles following the instructions on the package. Once cooked, drain them thoroughly and arrange individually to prevent sticking.

In a medium saucepan set over moderate heat, melt the butter. Sprinkle in the flour and whisk until a smooth paste forms. Slowly pour in the milk, stirring constantly until the mixture becomes thickened. Remove from heat and stir in ½ cup of the Parmesan along with the salt and white pepper.

In a separate bowl, blend the ricotta cheese with the egg, garlic, 2 cups of the mozzarella, and chopped parsley until fully combined.

Gently fold together the shrimp and crab meat in another bowl, ensuring even distribution.

Lightly grease a 9 x 13-inch baking dish. Spread about 1 cup of the prepared white sauce on the bottom. Lay three noodles side by side over the sauce. Spoon over one-third of the ricotta mixture and spread evenly, then layer with one-third of the seafood mixture. Repeat this layering process twice more.

Pour the remaining sauce over the top layer and sprinkle with the remaining mozzarella and Parmesan cheese.

Cover the baking dish with foil and place in a preheated 350°F (175°C) oven. Bake for 30 minutes. Remove the foil and continue baking for an additional 10 minutes or until the top is golden and bubbling.

Let the lasagna sit for 20 minutes before slicing to allow it to firm up and set properly.