Peel the butternut squash, halve, then remove the seeds.
Cut the squash into 1-inch cubes.
Steam squash until soft, about 10 minutes.
Mince chilies with some of the adobo sauce, and mash into a paste.
Scoop squash into mixing bowl and beat with chili paste, butter, salt, and pepper until smooth.
Put into buttered 2-quart baking dish and bake uncovered at 350 degrees F until hot, about 20 minutes. (Note this can be prepared a day ahead, covered, and refrigerated. Bring to room temperature before reheating.)