Combine the sweet potato, butter and brown sugar in a bowl and beat well.
In a separate bowl, combine the flour, baking powder and baking soda. Add the buttermilk.
Combine the sweet potato and flour mixtures. Fold in the pecans.
Turn the dough out on a lightly floured surface. Knead only for 8 strokes. Roll the dough out to 1/2-inch thickness. Cut with the floured rim of a glass or use a floured biscuit cutter.
Place on an ungreased cookie sheet and bake for 16-18 minutes until tops are browned and biscuits are flaky.