Heat the oven to 375 degrees F (190 degrees C).
Using a large chef's knife, cut the squash in half lengthwise and scoop out seeds with a spoon. Set each half cut side down on a cutting board and cut them crosswise in 3/8-inch slices.
Brush a heavy baking sheet generously with butter and oil. Line up the squash slices on the baking sheet and brush them. Sprinkle with sugar, salt, and pepper and tuck herbs around the slices.
Cover with foil and bake in the oven 30 minutes. Remove foil and continue baking until undersides are brown, about 15 minutes, then turn the slices.
Bake 5 to 15 minutes more until the squash is very tender, brown, and crispy around the edges, 50 to 60 minutes total. Don't hesitate to brush with more butter and oil during cooking if it looks dry. For serving, transfer to a platter or individual plates.