01 -
Preheat oven to 350°F (175°C). Cook lasagna noodles in salted water according to package directions; drain and set aside.
02 -
In a large skillet, melt butter over medium heat. Add chopped onion and minced garlic; cook for 3 to 4 minutes until softened.
03 -
Stir in flour and cook for 1 minute, stirring constantly to form a roux.
04 -
Gradually whisk in milk and chicken broth. Season with salt, pepper, basil, and oregano. Simmer for 5 to 7 minutes, whisking, until the sauce thickens.
05 -
Stir in grated Parmesan cheese off heat and set sauce aside.
06 -
In a separate bowl, mix ricotta cheese with egg until smooth and fully incorporated.
07 -
Spread a thin layer of sauce on the bottom of a 9x13-inch baking dish. Arrange 3 noodles lengthwise, top with half the ricotta mixture, half the shrimp and crab, spinach if using, and one third of the mozzarella.
08 -
Add another 3 noodles over the previous layer. Repeat with remaining ricotta, seafood, optional spinach, and another third of mozzarella cheese.
09 -
Place final 3 noodles on top. Pour remaining sauce evenly over the surface and sprinkle with the rest of the mozzarella cheese.
10 -
Cover the dish tightly with foil and bake for 30 minutes.
11 -
Remove foil and continue baking 10 to 15 minutes more, until the top is golden and the sauce is bubbling.
12 -
Allow the lasagna to rest for 10 minutes before slicing for best presentation.