Preheat Oven: Preheat your oven to 375°F (190°C).
Cook Noodles: Boil lasagna noodles according to package instructions, drain, and set aside.
Sauté Aromatics: In a large skillet, heat butter and olive oil over medium heat. Cook onions until soft, then add garlic for 30 seconds.
Make Cream Sauce: Sprinkle flour into the skillet and stir to form a roux. Slowly add broth and heavy cream while stirring until thickened.
Season: Stir in Italian seasoning, paprika, salt, and black pepper.
Add Seafood: Add shrimp and cook 3 minutes until pink. Fold in crab meat and lemon juice.
Assemble Lasagna: Spread a thin layer of sauce in a baking dish. Add a layer of noodles, seafood mixture, ricotta, and mozzarella. Repeat layers until the dish is full.
Top and Bake: Finish with remaining mozzarella and Parmesan. Bake 30–35 minutes until bubbly and golden.
Rest and Serve: Let rest 10 minutes before slicing. Garnish with fresh parsley.