1. Preheat oven to 375°F (190°C). Grease a 9x13-inch baking dish. 2. Cook lasagna noodles, then set aside. 3. Make the white sauce: melt butter, add garlic, flour, and heavy whipping cream. Simmer until thickened. 4. Mix chicken, ricotta, spinach, and mozzarella. 5. Layer the lasagna: noodles, white sauce, chicken mixture, and cheese. 6. Bake for 25 minutes covered, then 20 minutes uncovered.