Preheat oven to 450°F and oil a shallow baking pan(s).
Toss the squash with the oil until it is coated well and spread in one layer in pan(s). Roast the squash in the oven for about 10 minutes and season with sea salt. Stir squash and roast 10 minutes more, or until tender and beginning to turn golden.
While the squash is roasting, in a saucepan bring 2% milk to a simmer with rosemary. Heat milk mixture over low heat 10 minutes and pour into a bowl to set aside.
In a large heavy saucepan cook the garlic in butter over moderately low heat, stirring, until softened. Stir in whole wheat flour and cook the roux, stirring, for a few minutes. Remove the pan from the heat and whisk in milk mixture until smooth. Return the pan to heat and simmer sauce, whisking occasionally, about 10 minutes, or until thick. Stir in squash and salt and pepper to taste.
Reduce oven temperature to 375°F and spray a baking dish, (13x9x2).
Pour 1 cup sauce into baking dish 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 cup Parmesan. Make 1 more layer in same manner, beginning and ending with pasta.
Beat the 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 cup 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.