1 1/2 pounds pumpkin, peeled, seeded, and chopped
1 1/2 tablespoons extra-virgin olive oil, plus more for drizzling
3 large garlic cloves, chopped
1/2 cup ricotta
1/2 cup grated Parmigiano-Reggiano
1 1/2 teaspoons finely chopped fresh sage, plus 4 large whole leaves
1/4 teaspoon salt, plus more to taste
1/2 teaspoon freshly ground pepper, plus more to taste
1 package (8-ounce) oven-ready lasagna sheets
6 tablespoons unsalted butter
Preheat oven to 350 degrees F. Place pumpkin, along with 3/4 cup water, in a large skillet over medium heat. Cover and steam until tender, 20 minutes. Remove to a medium bowl and mash until smooth.
Heat 1 1/2 tablespoons olive oil in a small skillet and sautÃ© garlic until golden. Transfer garlic to a mortar and pestle, then crush to a paste. Stir cheeses, chopped sage, salt, pepper, and garlic paste into mashed pumpkin. Set aside.
Bring a large pot of water to boil. Cook lasagna sheets until tender, about 2 minutes. Transfer to a plate and drizzle with olive oil to prevent pasta from sticking together. Reserve 1/4 cup pasta water.
Liberally brush a medium baking dish with oil. Place a lasagna sheet on a clean work surface. Add 4 tablespoons pumpkin mixture to center of lasagna, roll into a cannelloni tube, then transfer to prepared baking dish. Repeat with remaining sheets.
Pour reserved pasta water over lasagna and cover tightly with foil. Bake until heated through and pasta is tender, 20 to 25 minutes. Cook butter and sage leaves in small skillet over medium-high heat until golden-brown. Drizzle over pumpkin cannelloni and serve immediately.