Whisk together the buttermilk, pumpkin and vanilla in a medium bowl until smooth. Add the wet mixture to the dry along with the cranberries and candied ginger. Mix until it is all just combined (do not over-mix or the scones will be tough).
Transfer to a lightly-floured surface and knead the dough gently 4 or 5 times. Pat the dough into a circle that is about 8 inches round and about 1 1/2 inches thick. Cut the circle in half, and then cut each half into 4 pie-shaped wedges (triangles). Place the scones on the baking sheet and brush the tops with the heavy cream.
Bake until golden brown and a toothpick inserted in the middle comes out with a few moist crumbs attached, 20 to 25 minutes. Let cool on a baking rack for 15 minutes before serving.
For the butter: Meanwhile, combine the cream, maple syrup and sea salt in the chilled bowl of a stand mixer fitted with the whisk attachment. Whip on low speed at first, then once the mixture begins to thicken, increase the speed and whip until light and fluffy and has turned into butter. Don't over-mix the butter or it will break.