Preheat the oven to 400ºF. Line a sheet pan with parchment paper.
Place the potatoes on the prepared sheet pan and cut a few slits in each potato to allow steam to escape. Bake the potatoes for 50 minutes to 1 hour, until very tender when tested with a skewer. Set aside for 10 minutes, until cool enough to handle.
Meanwhile, melt 1 ½ tablespoons of butter in a small skillet over medium heat. Add the red onion and sauté for 4 to 5 minutes, until tender. Add the thyme and cook for 1 minute. Set aside.
Cut the potatoes in half lengthwise and carefully scoop out some of the sweet potato into a medium bowl, leaving a ½-inch-thick shell of sweet potato. Sprinkle the potato shells with salt and pepper.
Add the egg, red onion, salt, and pepper to potato in medium bowl and stir until combined. Spoon the mixture into the sweet potato shells.
Return sweet potatoes to the oven and bake for 15 minutes.
Melt 4 Tablespoons of butter with maple syrup. Add pecans and cook for 5 minutes.
Remove potatoes from oven and pour Maple Pecan Butter onto the stuffed potatoes. Serve hot.