In a small bowl, dissolve the yeast and a pinch of sugar in warm water. Let it stand for about 5 to 10 minutes until the mixture becomes frothy.
In a large mixing bowl, combine the mashed sweet potatoes, yeast mixture, sugar, melted butter, salt, and egg. Mix well.
Gradually add in the flour, mixing until a soft dough forms. Knead the dough on a floured surface for about 8-10 minutes until smooth and elastic.
Place the dough in a lightly greased bowl, cover with a clean cloth, and let it rise in a warm place until it doubles in size, about 1 hour.
Punch down the dough and shape it into 12 rolls. Place them on a greased baking sheet or in a baking dish.
Cover the rolls and let them rise again for about 30 minutes until they are puffy.
Preheat the oven to 350°F (175°C). Bake the rolls for 20-25 minutes until golden brown.
Remove from the oven and let them cool on a wire rack. Serve warm.