Preheat your oven to 400 degrees F. Line a baking sheet with parchment paper.
Prick the sweet potatoes all over with a fork and bake until tender, about 30 to 40 minutes.
Remove from the oven and let cool to the touch for about 10 minutes.
Cut the potatoes in half lengthwise and scoop out the flesh into a medium bowl, lightly mash with a fork.
Cover the bowl and refrigerate until cool, at least 20 minutes.
Increase oven temperature to 425 degrees F. Line two baking sheets with parchment paper.
In a large bowl, whisk together the flour, sugar, baking powder, salt, cinnamon, and nutmeg.
Incorporate the butter into the flour mixture until crumbly, with lumps about the size of small peas.
Add the cooled sweet potatoes and ¼ cup of heavy cream, stirring into the flour mixture.
Add the remaining ¼ cup cream and buttermilk, stirring until just mixed.
Turn the dough out onto a lightly floured surface and knead a few times until cohesive.
Pat the dough into a rectangle about ¾ inch thick and cut into squares, then diagonally into triangles.
Transfer to prepared baking sheets and bake for 15 to 20 minutes until lightly golden.
Let the scones cool slightly, then prepare the glaze.
Whisk together the powdered sugar, maple syrup, heavy cream, and salt until smooth.
Drizzle the icing over warm scones and serve.
