Preheat oven to 425.
In a saucepan over high heat, cook sweet potatoes (in enough water to cover) to boiling, reduce heat to low, cover and simmer 12-15 minutes, until fork tender. Drain, mash, and set aside to cool.
In a large bowl, mix flour, brown sugar, baking powder, and salt.
Cut in butter with a pastry blender until mixture resembles coarse crumbles.
Stir in milk and cooled sweet potatoes (start with 1/3 cup of milk, and drizzle in more if dough is too dry and won't come together) and mix until dough is just combined.
Turn out onto a lightly floured surface, and cut dough in half. Roll each half into a circle, 1/4"-1/2" in thickness, and cut dough with a circle biscuit cutter. Or, pat each half of dough into a square and cut into equal pieces.
Makes between 20-25 biscuits.
Place biscuits 2" apart on 2 ungreased large cookie sheets.
Bake 12-15 minutes, or until golden brown.