Bake the sweet potato until it is tender, about 1 hour. When it's cool enough to handle, peel the potato and transfer it to a large bowl. Mash the sweet potato until it is very smooth. Stir in the green onions or raisins if you are using them and mix well.

Stir in 3 cups (750 ml) of flour, the dry milk, brown sugar, yeast, and salt. Stir in 1/2 cup of warm water and 2 tablespoons of oil until well combined. Turn the dough out onto lightly floured surface and knead until smooth, adding remaining ½ cup (125 ml) flour if necessary to make a fairly stiff dough that's slightly sticky.

Transfer the dough to lightly greased bowl. Cover the bowl and let the dough rise in a warm place until it is doubled in size, about 45 minutes. Punch the dough down, cover, and let it rise again until doubled, about 45 minutes.

Punch the dough down again and cut it into 12 pieces. Shape each piece into a ball and transfer them to a baking sheet lined with parchment, or look below for directions to make crescent rolls from the dough (as in the images). Cover and let rise until puffy, about 15 minutes.

Meanwhile, the preheat oven to 350°F (180°C). Brush the rolls with milk and bake them until they are golden brown and sound hollow when tapped on the bottom, which will be about 30 minutes.

Let them cool for 15 minutes before serving.