Preheat your oven to 400°F (200°C). Pierce each sweet potato several times with a fork, then place them on a baking sheet. Bake for 45 to 55 minutes, or until they are tender all the way through. Let them cool slightly so they’re easier to handle.
While the potatoes bake, make the walnut topping. In a small saucepan over medium-low heat, combine 1 tablespoon maple syrup with the chopped walnuts and brown sugar (if using). Stir frequently until the walnuts are coated and lightly toasted, about 4 to 5 minutes. Remove from heat and set aside.
Once the potatoes are cool enough to touch, slice each one in half lengthwise. Gently scoop out the flesh into a mixing bowl, leaving a small border around the edge to help the skins hold their shape. Add butter, cream, 2 tablespoons maple syrup, cinnamon, nutmeg, and a pinch of salt. Mash or mix until smooth and creamy.
Spoon the sweet potato filling back into each skin, mounding it slightly. Smooth the tops for even baking. If desired, lightly brush or spray the skins with olive oil to help them crisp up in the oven.
Return the stuffed sweet potatoes to the oven and bake at 375°F (190°C) for 15 to 20 minutes, or until warmed through and slightly golden on top.
Just before serving, sprinkle the maple walnut mixture generously over each sweet potato. Add a small pinch of flaky sea salt if you like a sweet-salty finish. Serve warm, and enjoy every cozy bite.