Preheat the oven to 375°F. Position a rack in the center of the oven.

In a small saucepan, melt the butter over medium heat. Add the sage and fry gently until the leaves turn a darker brown and feel somewhat firm to the touch, 2 to 3 minutes. Use a slotted spoon to transfer the leaves to a kitchen towel to drain. Add the walnuts to the butter and fry gently, until they turn slightly darker in color, 2 to 3 minutes. Transfer with a slotted spoon to the sage leaves and season with salt. Continue cooking the butter over medium-low heat until it turns light brown, another 2 to 3 minutes. Remove from the heat and cover to keep warm.

Place the squash on a flat surface and cut each in half lengthwise. Scrape out the seeds and discard. Arrange the halves, cut side up and in a single layer on a baking sheet, season with salt and pepper, and sprinkle with the brown sugar and molasses. Finish by combining the ginger, cinnamon, and cloves in a small fine mesh strainer and using it to dust the squash with an even layer of the spices. Spoon the brown butter over the squash. Fill the bottom of the baking sheet with about ½ inch water to create steam while the squash cooks. Cover the sheet with aluminum foil and seal the edges tightly.

Place the baking sheet in the center of the oven and bake, undisturbed, for 1½ hours. Pierce the squash with the tip of a small knife; it should be yielding and tender. If not, roast for 30 minutes more. Carefully peel back the foil and let cool.

Using a large spoon, scoop the flesh from the squash, taking care not to take any skin with it. Transfer to a blender. Add a few light grates of orange zest, then cut the orange in half and squeeze in all of the juice. Add the cream and puree until smooth. Pour the puree into a large sauté pan and season with salt and pepper. Cook gently over medium heat, whisking from time to time, to remove any excess water and intensify the flavor, 5 to 8 minutes.

Bring a large pot of water to a rolling boil. Add a generous amount of salt; the pasta water should taste like seawater. Add the farfalle and stir so it doesn’t stick to the bottom. Cook the pasta until al dente, chewy but not hard or raw tasting, 8 to 10 minutes. Reserve a little of the pasta water, then drain the pasta in a colander.

Add the pasta to the sauce and toss to combine. Taste for seasoning. Add a pinch more salt, pepper, and a little more brown sugar to amplify the flavors; add some pasta water if the sauce needs to be thinned.

Spoon the pasta and sauce into individual bowls and top with the fried walnuts and sage.