Stir together sweet potatoes, butter, and 1 cup milk until well blended. Add flour, baking soda, and sugar, stirring just until dry ingredients are moistened. Add remaining 1/4 cup milk to moisten dough, if needed.
Turn dough out onto a lightly floured surface; knead 8 to 10 times. Pat or roll dough to a 3/4-inch thickness; cut with a 2-inch round cutter. Place biscuits on lightly greased baking sheets.
Bake at 400° for 15 minutes or until golden brown.