1. Peel sweet potato, chop into chunks and place in a pot with cold water. Bring to a boil and and cook until potatoes are fork tender, about 20-25 minutes. Drain potatoes, then place in a bowl and mash.
2. In the bowl of an electric mixer, combine water, yeast, 2 tablespoons honey and olive oil. Mix with a spoon and let sit until foamy, about 15 minutes.
3. Once foamy, add potatoes, remaining honey, 4 tablespoons melted butter, buttermilk and salt. Gradually add flour with the mixer on low until a sticky dough forms, then knead with the dough hook for about 2-3 minutes. Brush a large bowl with melted butter, then place the dough in the bowl. Cover and let rise in a warm place for about 2 hours.
4. Using a bit of flour, knead dough until silky then divide in half. Roll into a long rope, then cut off pieces of dough (about 2 ounces each) and roll into a ball. Place them into a greased baking sheet. If desired, you can freeze dough at this point for up to 2 months. If baking immediately, cover the baking dish and let sit in a warm place to rise for about 30-45 more minutes.
5. Preheat oven to 375 degrees. Brush rolls with beaten egg, then bake for 20-25 minutes, or until the tops are slightly golden brown. Serve warm with butter and honey.