Preheat the oven to 350 degrees.
In a large mixing bowl, stir together the flour, brown sugar, baking powder, cinnamon, salt, ginger and allspice. Add the shortening and cut in with 2 knives until crumbly. Add the sweet potatoes and mix well with a wooden spoon. Add the cream and pecans and stir just until moistened.
Turn the dough out onto a lightly floured surface. Roll out the dough to one and one-half inches thick. Cut out with a 2-inch floured biscuit cutter. Place the biscuits 1 inch apart on ungreased baking sheets. Bake until golden brown, 25 to 30 minutes. Serve warm or let cool on a wire rack until room temperature.
Makes about 2 dozen biscuits