Step 1

Heat oven to 400°F. In 2-quart saucepan, melt butter over medium heat. Stir in flour with whisk; cook and stir 2 minutes. Slowly beat in broth, whipping cream, 3/4 teaspoon of the salt and the nutmeg with whisk. Increase heat to medium-high; heat to boiling, stirring constantly. Reduce heat; simmer 3 to 5 minutes, stirring occasionally, until thickened. Remove from heat.

Step 2

In 12-inch nonstick skillet, heat oil over high heat. Add mushrooms; cook 6 to 8 minutes, stirring frequently, until browned and any liquid from mushrooms has evaporated. Reduce heat to medium. Add garlic; cook and stir 1 minute. Gradually add spinach, stirring constantly, and cook until wilted. Remove from heat. Stir in 2 1/4 cups of the cream sauce. Reserve remaining sauce.

Step 3

In medium bowl, mix ricotta cheese, 2 cups of the mozzarella cheese, the Parmesan cheese, egg, remaining 1/2 teaspoon salt and the pepper.

Step 4

To assemble: Spray 13x9-inch (3-quart) glass baking dish with cooking spray. Spoon 3/4 cup of the sauce into bottom of baking dish. Top with 3 of the lasagna noodles in single layer. Evenly top with 1 cup of the cheese filling and 1 1/3 cups of the spinach mixture. Repeat layers twice, starting with noodles and ending with spinach mixture. For final layer, top with 3 noodles; pour remaining 3/4 cup sauce over top, and sprinkle with remaining 1 cup mozzarella cheese. Cover with foil; bake 20 minutes. Remove foil; bake 20 to 25 minutes or until heated through (165°F in center), bubbly and lightly browned. Let stand 15 minutes before cutting.

Step 5

To freeze: Line 13x9-inch (3-quart) glass baking dish with foil, making sure foil is as smooth as possible, as wrinkled foil may get stuck in sauce during freezing process. Leave enough overhang to be able to lift assembled lasagna out of dish. Spray foil with cooking spray. Cover and refrigerate sauce and spinach mixture 30 to 40 minutes before making cheese filling and assembling lasagna. Stir 2 1/4 cups cream sauce into spinach mixture. Assemble lasagna in dish as directed; cover tightly with another layer of foil. Freeze unbaked lasagna about 8 hours or until completely frozen. Transfer frozen lasagna to labeled 2-gallon resealable freezer plastic bag. Remove air; seal and freeze up to three months. To bake: Remove foil, and transfer to 13x9-inch (3-quart) glass baking dish sprayed with cooking spray. Cover and thaw in refrigerator until completely thawed, at least 48 hours. Heat oven to 400°F. Cover with foil and bake 20 minutes; remove foil. Bake 25 to 30 minutes or until heated through (165°F in center), bubbly and lightly browned. Let stand 15 minutes before cutting.