After trimming the ends, slice the squashes in half lengthwise. Scoop out the seeds and slice each half into quarters. (Save the seeds to make a toasted snack, or toss them into Roasted Acorn Squash Salad.)
Place the squash slices in a roasting pan and dot with the butter. Sprinkle with the brown sugar, salt, and pepper. Scatter on the thyme. Cover with foil and bake 20 minutes.
Remove the foil and roast 10 minutes more or until the squash is tender. Serve warm or at room temperature.