Heat oven to 400°. Combine flour, baking powder, salt, and baking soda in a large bowl. In a separate bowl, combine sweet potato, buttermilk, and maple syrup.

Use the large holes of a box grater to grate frozen butter into the flour mixture. Toss lightly to coat butter with flour. Add sweet potato mixture and mix gently until a shaggy dough forms. Turn dough onto a floured work surface and lightly knead until it just comes together in a lumpy mound.

Pat dough into a ¾-inch-thick circle. Cut out 3-inch circles and transfer to a baking sheet. Re-roll dough as necessary to make 8–10 biscuits. Brush tops with a little buttermilk. Bake until bottoms are golden, 12–15 minutes.