Heat the oven to 400ºF and arrange a rack in the middle. Heat the olive oil in a large pot over medium heat. When it shimmers, add the onion and garlic, season with salt and freshly ground black pepper, and cook until soft, stirring occasionally, about 5 minutes.
Add the cream and a few handfuls of greens and cook, stirring occasionally, until slightly wilted. Continue adding greens a little at a time until they all are slightly wilted. Cook, stirring occasionally, until the greens are tender, completely wilted, and coated in cream, about 10 minutes. Season with additional salt and freshly ground black pepper and remove from heat.
Spread 1 cup of the crème fraîche evenly over the bottom of a 13-by-9-inch baking dish. Cover with a layer of 4 noodles, allowing them to overlap slightly. Using a slotted spoon, scoop a third of the greens mixture from the cream and evenly spread it over the noodles, then cover with a third of the ricotta and a quarter of the Parmesan. Repeat to make two more layers, and end with a final layer of noodles on top. Evenly pour 1/4 cup of the warm cream over the noodles. Mix together the remaining crème fraîche and Parmesan and spread it evenly over top.
Cover the lasagna with foil and bake until bubbling and starting to brown, about 45 minutes. Remove the foil and bake until the top is browned completely and the sauce is bubbling, about 10 minutes more. Let cool at least 10 minutes before serving.Source : allrecipes.com