Fresh Spinach Ravioli Lasagna

Ingredients (13)

• 2 tablespoons unsalted butter
• 2 tablespoons all-purpose flour
• 3 cups coarsely chopped fresh spinach
• 2 cups whole milk
• Freshly grated nutmeg, to taste, optional
• kosher salt, to taste
• Freshly ground black pepper, to taste
• 3/4 cup grated Parmesan cheese, divided
• 1 1/2 cups ricotta cheese
• 1 teaspoon lemon zest
• 1 teaspoon minced garlic
• 3 (9-ounce) packages spinach-artichoke ravioli, or similar
• 1 (6-ounce) can artichoke hearts, drained and coarsely chopped