Preparation

• Position a rack in the center of the oven and heat the oven to 375°F.
• Generously butter a rimmed baking sheet. Cut the small pumpkin in half lengthwise and put it cut side down on the baking sheet. Cut a 1/2-inch lid from the stem end of the medium pumpkin and put both pieces cut side down on the same baking sheet. Cut the sweet potato in half lengthwise and place cut side down on the same baking sheet. Cover the vegetables tightly with foil and bake until the sweet potato and halved pumpkin are very tender, and the larger pumpkin is tender when pierced with fork, about 1-1/2 hours. Let stand until cool enough to handle.
• Scoop the seeds from the halved pumpkin and discard. Remove the skin and put the flesh in a food processor. Peel the sweet potato and add it to the processor, along with the butter, brown sugar, orange zest, and thyme. Purée until smooth and season to taste with salt and pepper.

  Scoop the seeds from the larger pumpkin, leaving the shell and flesh intact. Season the inside of the pumpkin lightly with salt and pepper. Transfer the purée to the pumpkin shell and top with the lid. (If you can’t fit all the purée, put the remainder in a small baking dish, cover, and bake alongside the pumpkin.) Put the pumpkin on the baking sheet and bake until the pumpkin and purée are heated through, about 40 minutes. Transfer to a serving plate and serve, spooning the purée from the pumpkin.