Preheat oven to 400°F. Place garlic on a piece of foil, drizzle with oil, season with salt and pepper and wrap in foil. Roast garlic 45 minutes to soft then let cool. Once cool, squish cloves from skins.
While garlic roasts, heat a medium pot or Dutch oven with a cover over medium-high heat with EVOO, 2 turns of the pan. Add squash and onions, and season with salt, white pepper and nutmeg. Cover pan and cook to tender, 12-15 minutes, stirring occasionally. Remove lid and add wine, letting it almost evaporate or reduce by 2/3. Add stock and stir then remove from heat. Add the roasted garlic to the pot along with the mascarpone.
In a small pan, melt the butter over medium heat. When it bubbles, add sage and crisp leaves while butter browns. Remove sage to a paper towel and reserve. When butter is deep, caramel brown and fragrant, add it to the pot with the squash. Purée sauce with an immersion blender or in 3 batches in a food processor.
For the sausage, heat 1 tablespoon EVOO, 1 turn of the pan, in a large skillet over medium-high heat. Add sausage and brown and finely crumble. Drain off excess fat and remove pan from heat.
For greens, heat remaining EVOO, 2 turns of pan, and crushed garlic in a large skillet over medium heat. Add greens in batches and wilt, season with salt, pepper and nutmeg. Sauté 2 minutes then douse with lemon juice and let cool. Drain greens of excess liquid and discard garlic clove.
In a large mixing bowl, combine ricotta with 1 cup grated parm, egg and cooled greens.
To assemble, ladle some sauce in the bottom of a lasagna pan. Build four layers of lasagna noodles, some greens and ricotta, and sausage. Finish with more butternut sauce and sprinkle the top with Fontina or Mozzarella and remaining 1/2 cup Parm. Cover with foil and cook about 25 minutes then remove foil and cook uncovered another 20 minutes until brown and bubbly.
Let cool 20 minutes, top with crispy sage leaves then cut to serve.
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