first you need to bake your potato. when the oven is hot put the potato in until cooked all the way through (about an hour depending on the size of your potato). when it's done take it out and cut it in half and scoop out 1 cup of the flesh. mash it well and let cool
in a large bowl, mix together the flour, cornmeal and baking powder. cut in the margarine until you have a coarse meal. add the potato, milk mixture and syrup and mix until combined (i would recommend using your hands for that bit) add nuts (if using) and mix again.
sprinkle dough with flour. pat dough so that it's about and inch thick and cut into biscuits. transfer to baking sheet. bake until tester inserted into center comes out clean, about 15 minutes.