- Preheat an oven to 400°F
- On a rimmed baking sheet, toss together the squash, onion and olive oil, then spread the squash mixture in a single layer. Cut 1 tablespoon of the butter into bits and dot the squash evenly. Season with salt and pepper. Roast, rotating the pan front to back about halfway through cooking, until the squash and onion are golden and tender, about 45 minutes.
- Bring a large pot three-fourths full of salted water to a boil over high heat. Add the pasta and cook until al dente, according to the package instructions. Drain, reserving 1 cup of the cooking water. Cover the pasta to keep it hot.
- Meanwhile, heat a large sauté pan over medium heat. Add the bacon and sauté until most of its fat is rendered and the bacon is crisp on the edges but still chewy at the center, 4 to 5 minutes. Pour off all but 1 tablespoon of the fat and return the pan to medium-high heat. Add the sage and sauté for 30 seconds. Add the squash and cook, stirring occasionally, until heated through, about 2 minutes. Stir in the pine nuts.
- Add the hot pasta, the remaining 2 tablespoons butter and 1/4 cup of the hot pasta water and stir to combine. If the pasta seems dry, stir in a little more pasta water.
- Season with salt and pepper. Transfer to a warmed serving dish and sprinkle the cheese on top. Serve immediately.