1. First, preheat your oven to 400°F (200°C).

2. Then, scrub the sweet potatoes clean and prick them several times with a fork.

3. Bake the sweet potatoes directly on the oven rack for 45-60 minutes, or until very tender.

4. Next, remove them from the oven and let them cool enough to handle.

5. Cut each sweet potato in half lengthwise.

6. Carefully scoop out the flesh into a large bowl, leaving a thin border in the skins to maintain their shape.

7. Add the melted butter, maple syrup, milk, cinnamon, nutmeg, and salt to the sweet potato flesh.

8. Mash everything together until smooth and creamy.

9. Taste and adjust seasonings as needed for your perfect Twice-Baked Sweet Potatoes with Maple and Walnut.

10. Stir in half of the chopped walnuts.

11. Spoon the sweet potato mixture back into the empty skins, mounding it slightly.

12. Sprinkle the remaining walnuts over the tops of your filled Twice-Baked Sweet Potatoes with Maple and Walnut.

13. Place the filled sweet potatoes back on a baking sheet.

14. Bake for another 15-20 minutes, or until heated through and lightly golden.

15. Serve these delightful Twice-Baked Sweet Potatoes with Maple and Walnut warm.