Preheat oven to 375 degrees F. Lightly butter a 9x13 inch baking dish.

On a baking sheet, toss together the butternut squash, olive oil, and a pinch each of salt and pepper. Transfer to the oven and roast for 25-30 minutes or until the squash is tender.

Meanwhile, make the sauce. Heat the butter, garlic, sage, and rosemary, in a large skillet over medium heat and cook until the butter begins to brown, about 3-4 minutes. Remove the sage and rosemary from the skillet. Whisk in the flour and cook for about 1 minute. Slowly add the milk and broth, whisking until combined. Stir in the nutmeg and season with salt and pepper. Bring to a boil and stir for 3-4 minutes. Stir in the gouda or fontina cheese and the spinach. Stir until the cheese is melted. Remove from the heat.

In a medium bowl, mash the roasted butternut squash until mostly smooth. Stir in the ricotta. Season with salt and pepper.

Spread 1/4 of the cheese sauce in the bottom of the prepared baking dish. Top with 3-4 lasagna sheets. Spread with 1/2 the butternut squash mixture, and then another 1/4 of the cheese sauce, and a handful of provolone. Repeat the layering until all the squash and sauce have been used. Arrange the prosciutto on top, if using. Bake uncovered for 45 minutes or until the top has bubbled up and browned a bit. Let stand 10 minutes before serving. Top with the reserved fried sage and rosemary. Enjoy!