3 lbs. butternut squash, peeled, seeded, and cut into 1/2 inch cubes (about 9 1/2 cups)
3 Tbs. vegetable oil
4 cups milk
2 Tbs. dried rosemary, crumbled
1 Tbs. minced garlic
1/2 stick (1/4 cup) unsalted butter
1/4 cup all-purpose flour
Nine 7-by 1 1/2-inch sheets dried no boil lasagna
1 1/3 cups freshly grated paremesan cheese
1 cup heavy cream
1/2 tsp. salt
Fresh rosemary sprigs, for garnish
Preheat oven to 450º F., and oil 2 large shallow baking pans. In a large bowl, toss squash with oil and salt until well coated, spread in one layer in the baking pans. Roast squash about 20 minutes, or until soft and golden, stir after 10 minutes. While squash is roasting, bring milk and rosemary to a simmer in saucepan. Cook milk mixture over low heat 10 minutes. Cool in pan until needed for sauce, then strain through sieve. In a large heavy saucepan, cook garlic in butter over low heat, stirring until soft – but not colored. Stir in flour and cook roux, stirring constantly, for 3 minutes. Remove pan from heat and add milk mixture in a stream, whisking until smooth. Return to heat and cook, stirring constantly, until thick – about 10 minutes. Stir in squash. Salt and pepper to taste. Reduce oven temperature to 375º F. Pour 1 cup sauce into baking dish (sauce may not cover completely) and cover with 3 lasagna sheets, making sure they do not touch. Spread half of remaining sauce over pasta and sprinkle with 1/2 cup Parmesan. Make 1 more layer in same manner with 3 lasagna sheets, remaining sauce, and 1/2 cup Parmesan. Top with remaining 3 lasagna sheets.
In the bowl of an electric mixer, beat cream with salt until it holds stiff peaks. Spread cream evenly over lasagna, making sure pasta is completely covered. Sprinkle remaining 1/3 cup Parmesan over cream. Bake, covered with foil in middle of oven, 30 minutes. Remove foil; push edge of lasagna noodles under topping, if necessary, and bake 10 minutes more, or until bubbling and golden. Let lasagna stand 5 minutes. Cut into squares and garnish with fresh rosemary.