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.