Start by preparing the sweet potato. Place it on a baking tray, coat it with oil, and use a fork to pierce it in a few spots. Roast the sweet potato in a preheated oven at 425°F for 45-50 minutes, or until it becomes tender when pierced with a fork.

Once the sweet potato is cooked, take it out of the oven, allow it to cool slightly, and peel it completely. Mash the flesh with a fork until smooth, then set it aside.

In a separate bowl, combine the warm water, sugar, and salt. Stir until dissolved. Add the active dry yeast to this mixture, stir, and let it sit in a warm area for about 10-15 minutes, or until it becomes frothy.

In the bowl of a stand mixer, or a large mixing bowl if doing it by hand, combine the flour, salt, mashed sweet potato, and unsalted butter. Once the yeast mixture is frothy, add it to the bowl.

Using the dough hook attachment on the stand mixer, knead the dough for about 5 minutes, until it forms a smooth, cohesive ball. If kneading by hand, continue kneading until the dough is soft and elastic.

Shape the dough into a ball, coat a clean bowl with a little oil, and place the dough inside. Cover and allow it to rise in a warm, draft-free spot for 60-70 minutes, or until it has doubled in size.

Once the dough has risen, punch it down to remove any air bubbles. Knead it gently for a couple of minutes on a lightly floured surface.

Shape the dough into a rectangle about 8 inches wide. Starting from the shorter side, roll the dough into a tight log. Grease a 9x4-inch bread pan, place the dough log inside, and cover it. Let the dough rise for another hour, or until it has nearly reached the top of the pan.

Preheat your oven to 425°F. Once the dough has risen, lightly spray the top with oil. Bake for 22-24 minutes until golden brown.

Remove the bread from the oven, allow it to cool slightly in the pan before transferring it to a cooling rack. Once fully cooled, slice to your desired thickness and enjoy.