Oven at 375 degrees.
Place the squash onto a lined baking sheet. Toss with the salt, cinnamon, nutmeg and enough olive oil to coat. Cook for about 25-30 minutes until fork tender and lightly browned.
Place half the roasted squash with into a food processor (I threw all of it in so do as I say not as I do, it was too much at once). Process until relatively smooth, some chunks are just fine.
In a bowl combine the pureed butternut squash, the ricotta and egg.
While the squash is roasting you can make the sauce. In a medium saucepan, over medium heat, add in the butter. Once melted go ahead and whisk in the flour. Continue whisking and allow to cook for a minute.
Add in the slightly warmed milk and continue to whisk to remove any lumps. Continue to cook, stirring occasionally until thick enough to coat a spoon. Add in the grated cheese and stir to combine. Season with salt and pepper.
Ok, the components are ready to go, lasagna noodles cooked to al dente, sauce made and butternut squash filling made. Lets assemble!
I used my 12×9 inch (3 qt) Le Creuset baking pan. Add a thin layer of sauce to the bottom of the pan. Follow with a layer of noodles, butternut squash filling then a sprinkle of the shredded mozzarella. Keep in mind, keep the sauce layers thin, not looking for a gooey mess.
Continue with the remaining ingredients. End it off with noodles, sauce, mozzarella and a bit of grated cheese. You may have a few noodles extra… you can go ahead and roll those up and scrap the sauce that remains in the pot at the end of assembly, heck its one of my favorite parts of making lasagna.
Bake for 35-45 minutes until bubbly and the cheese golden and beautiful. I served mine with broccoli rabe and a spinach salad.