Direction

1. Preheat oven to 425°F with racks in upper third and lower third positions. Slice butternut squash halves crosswise into 1/4-inch-thick slices; place in a large bowl. Toss butternut squash with 2 tablespoons oil and 1/4 teaspoon each salt and pepper until evenly coated. Divide butternut squash between 2 large rimmed baking sheets. Bake until tender and lightly browned, 20 to 25 minutes, rotating baking sheets from top to bottom racks halfway through baking time. Let cool until room temperature, about 30 minutes. Reduce oven temperature to 400°F.
2. Meanwhile, heat remaining 1 tablespoon oil in a large skillet over medium-high. Add mushrooms, and arrange in a single layer; cook, undisturbed, until browned, about 4 minutes. Stir; continue cooking, stirring occasionally, until mushrooms are evenly browned all over, about 3 minutes. Add spinach, and cook, tossing constantly, until wilted, about 1 minute. Remove from heat.
3. Melt butter in a large saucepan over medium. Add garlic and rosemary; cook, stirring often, until fragrant but not browned, about 2 minutes. Add flour; cook, whisking constantly, until lightly golden, about 1 minute. Gradually add milk, whisking constantly, until fully combined. Bring to a simmer over medium; cook, whisking often, until thickened, about 4 minutes. Gradually add Asiago cheese, whisking constantly, until melted and thick enough to coat the back of a spoon, about 2 minutes. Stir in salt and pepper. Remove from heat.
4. To assemble the lasagna, coat a 9- x 13-inch baking dish with cooking spray. Stir together ricotta, egg, lemon zest, and salt in a medium bowl. Spread 1/2 cup Asiago-Garlic Mornay Sauce on bottom of baking dish; top with 3 to 4 noodles (breaking noodles if needed to fit or cover). Spread 1 cup Asiago-Garlic Mornay Sauce over noodles; sprinkle evenly with half (about 1 cup) of mushroom mixture. Dollop 1 cup ricotta mixture over mushrooms, and spread out as evenly as possible. Top with half (about 1 1/2 cups) of butternut squash, and spread it in a single layer. Top with 6 slices mozzarella cheese and 2 tablespoons Asiago cheese. Repeat layers once, starting and ending with noodles. Pour remaining 1 1/2 cups Asiago-Garlic Mornay Sauce over final layer of noodles. Top with remaining 6 slices mozzarella cheese and 1/4 cup Asiago cheese. Cover tightly using aluminum foil; place on a large rimmed baking sheet.
5. Bake at 400°F on upper rack until sides of lasagna are bubbly, about 50 minutes. Uncover and bake at 400°F until cheese is browned and noodles are tender, about 20 minutes more.
6. Remove from oven, and let stand 15 minutes before slicing. Sprinkle with parsley.