This dish is easy to divide into make-ahead steps. Roast squash and prepare white sauce the night before, then layer lasagna up to six hours before the party. Just before guests arrive, top with cream and the last layering of Parmesan cheese, then bake.
3/4 cup (3 ounces) grated fresh Parmigiano-Reggiano, divided
1/2 cup whipping cream
How to Make It
Preheat oven to 450°.
Arrange butternut squash in a single layer in a large roasting pan coated with cooking spray. Coat squash with cooking spray. Bake at 450° for 25 minutes or until squash is just tender, stirring once. Set aside.
Lower oven temperature to 350°.
Combine 3 1/2 cups milk and rosemary in a 1-quart glass measuring cup, and microwave at high 5 minutes or until mixture begins to boil. Let stand 10 minutes. Strain milk through a fine sieve into a bowl; discard rosemary.
Lightly spoon all-purpose flour into a dry measuring cup; level with a knife. Combine flour and remaining 1/2 cup milk, stirring flour mixture with a whisk until well blended to form a slurry.
Melt butter in a large saucepan over medium heat. Add garlic; cook 1 minute or until tender, stirring constantly. Stir in steeped milk, and increase heat to medium-high. Gradually add slurry to pan, stirring constantly with a whisk. Cook 15 minutes or until thick, stirring frequently. Remove from heat; stir in 3/4 teaspoon salt and pepper. Combine milk mixture and squash, tossing gently.
Spread about 1 1/2 cups squash mixture into the bottom of an 11 x 7-inch baking dish coated with cooking spray. Arrange 3 noodles over squash mixture; top with 2 cups squash mixture and 1/4 cup cheese. Repeat layers once with 3 noodles, 2 cups of squash, and 1/4 cup of cheese. Top with 3 noodles.
Beat whipping cream and remaining 3/4 teaspoon salt with mixer at high speed until soft peaks form. Spread the whipping cream mixture over noodles; sprinkle with remaining 1/4 cup cheese. Cover with foil coated with cooking spray. Bake at 350° for 30 minutes. Uncover and bake an additional 15 minutes or until golden. Let stand 10 minutes.