Creamy Seafood Lasagna with Shrimp and Crab

Ingredients

• 9 lasagna noodles
• 2 tablespoons unsalted butter
• 1 small onion, finely chopped
• 2 cloves garlic, minced
• 1/4 cup all-purpose flour
• 2 cups whole milk
• 1 cup chicken broth
• 1/2 teaspoon kosher salt
• 1/4 teaspoon freshly ground black pepper
• 1/4 teaspoon dried basil
• 1/4 teaspoon dried oregano
• 1/2 cup grated Parmesan cheese
• 1 cup shredded mozzarella cheese
• 1 cup ricotta cheese
• 1 large egg
• 1/2 pound cooked shrimp, peeled and chopped
• 1/2 pound imitation crab meat, chopped
• 1/2 cup chopped spinach (optional)