Prick sweet potatoes several times with a fork. Place on a lined cookie sheet and bake for 1 hour, or until tender. Cool slightly.
Slice sweet potatoes in half lengthwise and scoop potatoes into the bowl of a stand mixer, being careful to keep skins intact.
Mix sweet potatoes on medium speed until creamy. Add in cream cheese, sour cream, 2 tablespoons brown sugar, and 1/2 teaspoon each of cinnamon, nutmeg and cloves.
Scoop filling back into skins evenly.
In a small bowl, stir together butter, remaining 1/4 cup brown sugar, walnuts, and remaining 1/2 teaspoon each of cinnamon, nutmeg and cloves.
Sprinkle walnut mixture evenly over filling in skins.
Return to oven and bake for 15 minutes. Serve with a drizzle of maple syrup.
