Preheat oven to 400 degrees F.
Line a baking sheet with a silpat (a French nonstick baking mat) or parchment paper. In a small bowl, combine melted butter and strip of orange rind; set aside.
In a medium bowl, combine flour, baking powder, baking soda, salt, brown sugar, ginger, and grated zest. Using a pastry cutter or 2 knives, cut the chilled butter into the flour mixture until it resembles coarse meal.
Make a well in the center and add sweet potato. Using a fork, stir in the sweet potato. Add buttermilk and stir just until the dough comes together. Do not over mix.
Lightly dust dough with flour. Turn dough onto a lightly floured surface, and knead gently 6 to 8 times.
On a clean work surface, pat out the dough to a thickness of 1/2-inch. Using a floured 1 1/2-inch or 2-inch biscuit cutter, cut out the biscuits as close together as possible. Transfer to prepared baking sheet. The scraps may be patted out again once more. Prick the tops of each biscuit a few times. Brush the tops with the reserved orange-flavored butter. Bake until golden brown, 15 to 18 minutes for the small biscuits and 20 to 25 minutes for the large biscuits.
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