Position racks in the upper and lower thirds of the oven and preheat to 450 degrees . Halve the squash lengthwise and discard the seeds. Pare off some of the peel to create stripes. Cut the squash crosswise into 1/2-inch-thick slices.
Divide the squash between 2 baking sheets. Brush the tops lightly with the EVOO and sprinkle with the sugar and 3/4 tsp. salt; season with pepper. Roast, switching and rotating the pans halfway through cooking, until tender and browned on the bottom, 18 to 20 minutes. Let the squash sit on the pans for 5 minutes, then transfer browned side up to a platter.
Meanwhile, in a small skillet, cook the butter over medium heat until the foaming subsides and the butter browns, about 2 minutes. Spoon the butter over the squash.