In a medium saucepan, cook the whole sweet potato in boiling (unsalted)
water until tender when pierced with the tip of a sharp knife,
about 20 minutes. Let the sweet potato cool, then pare it and
mash until smooth. You should have about 1 cup mashed sweet potato.
Let the cooking water cool to warm (105 deg. or less).
Position a rack in the center of the oven and preheat to 425 degrees.
In a medium saucepan, stir the mashed sweet potato with the melted
butter until smooth. Transfer the mixture to a medium bowl. Stir
in the milk, sugar, and egg. Sift the cake and all-purpose flours,
baking powder, and salt into a medium bowl, and then stir into
the liquids to combine. Knead briefly in the bowl to form a soft
dough.
On a floured work surface, roll out the dough to 3/4 inch thickness.
Using a 2 1/2 inch round cookie cutter, cut out biscuits. Gather
up the scraps, reroll, and repeat the procedure until 12 biscuits
are cut out. Transfer the biscuits to an ungreased baking sheet.
Bake the biscuits until golden brown, 15 to 20 minutes. Serve
hot, warm, or at room temperature.
Makes about 12 biscuits.
From "Kwanzaa" by Eric V. Copage