Rinse sweet potato very well and cook by boiling in water till soft. Or prick the sweet potato all over with a fork. Place on a microwave-safe plate and microwave at least four minutes, turning halfway through, until a knife cuts easily through the center. Cut in half and let cool before scooping out the flesh and discarding the skin. Mash the potato till there are no lumps or puree the potato in a food processor or blender.

Combine the buttermilk, margarine or butter, eggs, honey, yeast, and sweet potato in a large bowl if kneading by hand or the bowl of a stand mixer if kneading by the mixer. Add the salt and about two cups of the flour and stir with a wooden spoon. It will look rough and shaggy.

IF KNEADING BY HAND: Add in the remaining bread flour, kneading until a dough begins to forms. Continue kneading seven to nine minutes until a soft, smooth ball of dough is formed. The dough should feel elastic and slightly tacky. If the dough is unbearably sticky, add more flour about one tablespoon at a time. (I do about 600 grams bread flour that is about 4 3/4 cups bread flour and add more if needed)

IF KNEADING WITH MIXER: Attach the dough hook to the mixer, turn to medium-low speed, and gradually add in the remaining bread flour, kneading until a  dough begins to forms. Continue kneading on medium-high speed for 4 to 5 minutes until a soft, smooth ball of dough is formed. The dough should feel elastic and slightly tacky. If the dough is unbearably sticky, add more about one tablespoon of bread flour at a time.

Lightly grease a large clean bowl and place the dough in the bowl. Cover the bowl lightly with plastic wrap. Let rise for about  forty-five minutes to an hour room temperature or until the dough is doubled in size.

After the rising time is up, grease a 13×9-inch baking pan and set aside.  Deflate the dough and divide the dough into 15 equal pieces using a sharp knife or pizza cutter. Shape each piece into a ball and place in the prepared pan. Brush the rolls all over with the egg wash. Lightly cover the dough with plastic wrap and let the rolls rise for thirty minutes or more, or until about doubled in size.

Meanwhile, preheat the oven to  190°C or 375°F. Bake the rolls for twenty to twenty-five minutes, or until golden brown. Serve warm. Store leftovers in a plastic bag for up to 3 days.