Preheat the oven to 425 degrees. Line a baking sheet with parchment paper.

In a small bowl, whisk together the mashed sweet potatoes and 1/3 cup milk. Set aside.

In the bowl of a food processor fitted with the metal blade, combine the flour, sugar, baking powder and salt; process for a few seconds to mix. Add the chunks of cold butter, then pulse a few times until the mixture resembles coarse meal with some pea-size chunks of butter within. (If you don't have a food processor, this can be done by hand with a pastry cutter or your hands.)

Transfer the flour mixture to a medium bowl, then add the sweet potato mixture and fold gently to combine. Add the remaining 3 tablespoons milk a little at a time until the dough is just moistened and holds together (you may not need all of it).

Sprinkle a small handful of flour on a work surface. Turn the dough out onto the surface and knead lightly 2 or 3 times with the palm of your hand until the mixture comes together. Pat the dough into a 3/4-inch round. Using a 2-1/2 inch-round biscuit cutter or glass, cut the dough into biscuits. Gently press the scraps into another round and cut out more biscuits. Place the biscuits onto the prepared baking sheet and bake until golden on the bottom and firm to the touch, 12-14 minutes. Serve warm with honey butter.