Roasted Butternut Squash with Onions, Brown Butter and Sage

One 3 1/2-pound butternut squash—peeled, halved, seeded and cut into 1/2-inch pieces
2 medium onions, cut into 1/2-inch pieces
2 tablespoons extra-virgin olive oil
2 tablespoons packed dark brown sugar
Salt and freshly ground pepper
4 tablespoons unsalted butter
32 fresh sage leaves

Preheat the oven to 400°. In a large bowl, toss the squash with the onions, olive oil and brown sugar; season with salt and pepper. Spread the squash on a baking sheet. Roast for 1 hour, or until the squash and onions are tender and browned on the edges. Transfer the vegetables to a serving bowl.
Set a small skillet over moderately high heat. When it is hot, add the butter and cook until bubbling, about 3 minutes. Add the sage leaves and cook for about 2 minutes, until the butter is browned and the leaves are crisp. Season the browned butter and sage with salt, pour over the squash and serve warm.