Butternut Squash, Caramelized Onion, and Spinach Lasagna

INGREDIENTS

• 6 cups (1/2-inch) cubed peeled butternut squash
• 2 tablespoons extra-virgin olive oil, divided
• 2 tablespoons chopped fresh sage
• 12 garlic cloves, unpeeled (about 1 head)
• 1 teaspoon kosher salt, divided
• 1/2 teaspoon black pepper
• Cooking spray
• 1 large onion, vertically sliced
• 2 tablespoons water
• 2 (9-ounce) packages fresh spinach
• 5 cups 1% low-fat milk, divided
• 1 bay leaf
• 1 thyme sprig
• 5 tablespoons all-purpose flour
• 1 1/2 cups (6 ounces) shredded fontina cheese, divided
• 3/8 teaspoon ground red pepper
• 1/4 teaspoon grated whole nutmeg
• 9 no-boil lasagna noodles