Preheat oven to 450 degrees.

In a large bowl toss squash with oil until coated well and spread in one layer in baking sheet. Roast squash in oven 10 minutes and season with salt. Stir squash and roast 10 to 15 minutes more, or until tender and beginning to turn golden.

While squash is roasting, bring milk to a simmer with rosemary in a saucepan. Heat milk mixture over low heat 10 minutes and pour through a sieve into a large bowl.

In a large heavy saucepan cook garlic in butter over moderately low heat, stirring, until softened. Stir in flour and cook roux, stirring, 3 minutes. Remove pan from heat and whisk in milk mixture until smooth. Return pan to heat and simmer sauce, whisking occasionally, about 10 minutes, or until thick. Stir in squash and salt and pepper to taste.

Reduce temperature to 375°F. and butter a 13x9x2 baking dish.

Pour 1 cup sauce into baking dish (sauce will not cover bottom completely) and cover with 3 lasagne sheets, making sure they do not touch each other. Spread half of remaining sauce over pasta and sprinkle with 1/2 c. Parmesan. Make 1 more layer in same manner, beginning and ending with pasta.

In a bowl with an electric mixer beat cream with salt until it holds soft peaks and spread evenly over top pasta layer, making sure pasta is completely covered. Sprinkle remaining 1/3 c. Parmesan over cream. Cover dish tightly with foil, tenting slightly to prevent foil from touching top layer, and bake in middle of oven 30 minutes. Remove foil and bake lasagne 10 minutes more, or until top is bubbling and golden. Let lasagne stand 5 minutes.