Squash filling and peppery greens are placedinthe center of sheets of pasta, which are rolled into thetubular cannelloni shape, sealing the vegetables inside. Servethe finished dish with red wine and rustic bread.
To make filling, heat 2 tablespoons butter in a large skillet with sides over medium heat. Add onion; cook until it begins to soften, about 3 minutes. Add squash cubes; cook, stirring occasionally, until they begin to soften, about 5 minutes. Add cinnamon, nutmeg, cayenne pepper, cumin, 1 1/2 teaspoons salt, 1/4 teaspoon black pepper, and 1 cup water. Reduce heat, cover, and cook, stirring occasionally, until very tender, about 20 minutes.
Mash mixture with potato masher or wooden spoon, and transfer to a medium bowl to cool. When cool, stir in Parmesan and ricotta. Set aside in refrigerator until ready to assemble.
Wash the spinach or greens well. Remove and discard stems. Roughly chop spinach into smaller pieces. Heat remaining tablespoon butter in a large skillet over medium heat. Add spinach a little at a time; cook, tossing, until wilted and any liquid has evaporated. Season with 1 teaspoon salt and 1/4 teaspoon black pepper. Refrigerate until ready to assemble.
Heat oven to 375 degrees. Bring a large pot of water to a boil. Add the olive oil and remaining tablespoon coarse salt. One at a time, add pasta sheets to boiling water, and cook until al dente, 2 to 3 minutes less than manufacturer's instructions. Remove the pasta sheets with tongs, and drain them in a colander.
To assemble the cannelloni, lay out the pasta sheets on work surface. Spoon about 1/2 cup filling down the center of a sheet, and top with a heaping tablespoon of spinach. Brush one long side of pasta with water, roll up, starting with other long side, and seal. Repeat with the remaining pasta and filling. Spread half of the sage-walnut cream sauce in the bottom of a 9-by-13-by-2-inch baking dish. Place the cannelloni in the bottom of the dish, and cover with remaining sauce. Garnish with a few sage leaves. Bake until top starts to brown and filling is bubbling, about 30 minutes. Serve.