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1
Preheat oven to 450 and oil 2 large shallow baking pans.
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2
Roast squash: Toss squash with oil to coat. Spread in one layer. Roast for 10 minutes and season with salt. Stir and roast 10-15 minutes more until tender and turning golden brown
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3
Make a white sauce: While squash is roasting, bring milk and rosemary to a simmer about 10 minutes over low heat. Pour through sieve into a large pitcher. In a heavy saucepan, cook the garlic in butter until soft. Stir in the flour and cook the roux, stirring about 3 minutes. Remove from heat and whisk in the milk mixture in a stream until smooth. Return pan to heat and simmer sauce, whisking occasionally, about 10 minutes until thickened. Stir in roasted squash. Add salt and pepper to taste. Sauce may be made up to 3 days ahead, cooled, and the surface covered with plastic wrap.
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4
Reduce oven temperature to 375 and butter a 13x9 dish.
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5
Assemble lasagne layers: Pour 1 cup of the sauce into the bottom of the casserole dish. Cover with 3 sheets of lasagne, not touching. Spread 1/2 of the remaining sauce over the lasagne and sprinkle with 1/2 cup of parmesan cheese. Make 1 more layer- beginning and ending with lasagne sheets. Beat cream with salt to soft peaks. Spread over the pasta, covering completely. Sprinkle with the last 1/3 cup of parmesan cheese. Cover with foil, tenting slightly.
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6
Bake in the middle of the oven for 30 minutes.
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7
Uncover and bake 10 minutes more until top is bubbling and golden.
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8
Let it stand for 5 minutes.
