Combine the water and yeast in a large mixing bowl and let stand until the yeast is dissolved. Add the mashed sweet potatoes,milk, melted butter, brown sugar, and salt. Stir until all ingredients are evenly combined. Add the flour, stirring until a shaggy dough is formed and no more dry flour is visible. This dough will be very sticky.
Cover with plastic wrap or a clean kitchen towel and let stand until doubled in bulk, at least 2 hours or as long as 5 hours. Refrigerate from 2-24 hours.
When ready to shape the rolls, sprinkle your work surface with a little flour and turn the dough out on top. Sprinkle a little more flour on top and press the dough into a thick disk. Use a bench scraper or knife to divide the dough into 24 pieces. Shape into balls and place about 5 inches apart on a parchment-lined baking sheet. Cover and allow to rise until the rolls are roughly doubled in size, about 45 minutes in a warm kitchen.
About 20 minutes before the rolls are finished rising, preheat the oven to 400° Fahrenheit.
Remove the cover and bake the rolls for 20-25 minutes, until they are puffed and toasted brown. Serve warm or room temperature. Rolls are best the first day, but will stay fresh for several days after if stored in an airtight container.
• To make the mashed sweet potatoes, roast a medium-sized (roughly 9 ounce) sweet potato in a 400° oven until completely soft. Strip off the skin and mash.
• For extra richness, brush the tops with melted butter or egg yolk before baking. So good!
• These rolls can also be frozen if you're making them ahead of time. Allow the baked rolls to cool completely, wrap them in aluminum foil, and freeze them. To re-heat, let them thaw on the counter and then warm them in a 300° oven for 15 minutes.
Preparation time includes rising and refrigeration time.