Combine squash, 1 tablespoon oil, sage, garlic, 1/2 teaspoon salt, and black pepper in a large bowl; toss to coat. Arrange squash mixture on a baking sheet coated with cooking spray. Bake at 425° for 30 minutes or until squash is tender. Cool slightly; peel garlic. Place squash and garlic in a bowl; partially mash with a fork.
Heat remaining 1 tablespoon oil in a large Dutch oven over medium-high heat. Add onion, and sauté for 4 minutes. Reduce heat to medium-low; continue cooking for 20 minutes or until golden brown, stirring frequently. Place onion in a bowl.
Add 2 tablespoons water and spinach to Dutch oven; increase heat to high. Cover and cook 2 minutes or until spinach wilts. Drain in a colander; cool. Squeeze excess liquid from spinach. Add spinach to onions.
Heat 4 1/2 cups milk, bay leaf, and thyme in a medium saucepan over medium-high heat. Bring to a boil; remove from heat. Let stand for 10 minutes. Discard bay leaf and thyme. Return pan to medium heat. Combine remaining 1/2 cup milk and flour in a small bowl. Add to pan, stirring with a whisk until blended. Bring to a boil; reduce heat, and simmer for 5 minutes or until thickened, stirring constantly. Remove from heat; stir in remaining 1/2 teaspoon salt, 1 1/4 cups cheese, red pepper, and nutmeg.
Spread 1/2 cup milk mixture in bottom of a 13 x 9-inch glass or ceramic baking dish coated with cooking spray. Arrange 3 noodles over milk mixture; top with half of squash mixture, half of spinach mixture, and 3/4 cup milk mixture. Repeat layers, ending with noodles. Spread remaining milk mixture over noodles. Bake at 425° for 30 minutes, and remove from oven. Sprinkle with remaining 1/4 cup cheese.
Broil 2 minutes or until cheese is melted and lightly browned. Let stand 10 minutes before serving.
This was amazingly good - the whole family loved it (and typically aren't fans of butternut squash like I am). Yes, it does take awhile to prepare. I microwaved the milk so it was already hot when I set it on the burner. I steamed the spinach in the saute pan, then let it drain while I prepared the onions using the same pan to save on clean up. I also roasted the garlic as a whole head, cut off the end, drizzled olive oil then wrapped in foil while the squash baked, then squeezed the cloves out before mashing together. It worked well. We will definitely have this again.
Very labor intensive, as other have noted, but definitely not 3 hours. I used frozen spinach instead, so while that was defrosting in the microwave, I chopped the stuff for the squash. While the squash was roasting, I sliced the onions and got the milk, thyme, and bay leaf in pot. I also started cooking the onions. While the onions and squash continued to cook, I shredded the cheese. Once the onions and squash were both cooked, I started the milk. While the milk sat, I peeled the garlic and smashed it with the squash. I drained the spinach and stired it into the onions. Then I added the flour mixture to the milk - this was the only thing that took a while (and I consider downtime) because it just took forever to come back to a boil and thicken. It took about an hour to do all that plus 30 minutes cooking time.
It's a lot of work and the result is just ok. Probably won't be making again. Sounded fantastic, but it didn't turn out to be anything special.
Absolutely delicious. Hubby, kids & I LOVED it! I read all of the reviews so made sure to multitask so it didn't take 3 hours. I also used one pan for everything except the spinach, and one big bowl where I combined the spinach with the butternut squash and onions. I minced the 12 cloves of garlic and tossed it with the squash before roasting. I then added the remaining whole cloves of garlic from the head. This is a very flavorful dish and I will definitely make it again. Yummy and totally worth the effort!