Prep the oven and pan: Heat the oven to 375°F (190°C). Lightly grease a 9x13-inch baking dish with olive oil or nonstick spray.
Cook the spinach: In a large skillet, warm the olive oil over medium heat.
Add the garlic and cook 30 seconds until fragrant. Add the spinach with a pinch of salt and pepper. Sauté just until wilted, 2–3 minutes.
If using frozen spinach, squeeze it very dry before stirring it in to warm.
Make the creamy sauce: In a saucepan, melt the butter over medium heat. Whisk in the flour and cook 1 minute. Slowly whisk in the broth until smooth, then add the cream.
Simmer 2–3 minutes until slightly thickened. Stir in 3/4 cup Parmesan, Italian seasoning, a pinch of salt, and black pepper. Taste and adjust seasoning.
Warm the marinara: In a small bowl or saucepan, gently warm the marinara so it spreads easily.
This helps everything bake evenly.
Layer 1: Spoon a thin layer of marinara into the baking dish. Add a single layer of ravioli (no need to boil first). Top with a handful of sautéed spinach, a ladle of creamy sauce, and a sprinkle of mozzarella.
Layer 2: Repeat with marinara, ravioli, spinach, creamy sauce, and mozzarella.
Continue layering until you run out, finishing with creamy sauce and a generous blanket of mozzarella.
Top and season: Sprinkle remaining 1/4 cup Parmesan over the top. Add red pepper flakes if using. A light drizzle of olive oil helps browning.
Bake: Cover the dish loosely with foil (tent so cheese doesn’t stick).
Bake 20 minutes. Remove foil and bake another 15–20 minutes, until bubbly and golden at the edges.
Rest and garnish: Let the lasagna rest 10 minutes to set. Sprinkle with chopped basil or parsley before serving.
Serve: Pair with a simple salad and crusty bread.
A squeeze of lemon over the salad balances the richness nicely.