In a large mixing bowl, combine the warm milk, sugar, and yeast. Stir to dissolve the sugar and let sit for 5 minutes until frothy.

1. In a separate bowl, whisk together the flour, salt, cinnamon, and nutmeg.
2. Add mashed sweet potato, melted butter, and egg to the yeast mixture. Stir to combine, then gradually add dry ingredients, mixing until the dough forms. Add more flour if dough is too sticky.
3. Knead dough on a lightly floured surface for 5-7 minutes until smooth and elastic.
4. Place dough in a greased bowl, cover with a towel, and let rise for 1-1.5 hours until doubled in size.
5. Mix softened butter, brown sugar, cinnamon, and a pinch of salt in a small bowl for the filling.
6. Punch down dough and roll it into a 12×18-inch rectangle on a floured surface.
7. Spread the cinnamon filling evenly over the dough, leaving a border around the edges.
8. Roll dough into a log, slice into 12 equal pieces, and place them in a greased 9×13-inch baking dish.
9. Cover with a towel and let rise for another 30 minutes until puffy.
10. Preheat oven to 350°F (175°C). Bake for 20-25 minutes until golden brown and set in the center.
11. Whisk together powdered sugar, milk, and vanilla extract for the icing, and drizzle over rolls once they cool slightly.
12. Serve warm and enjoy!