Put the flour, bread starter or leaven, 20g of butter, honey, salt, and black sesame seeds into a bowl. Add water while stirring. Knead the dough for 10-15 minutes until it comes together as a lump. Cover with plastic wrap and let it rise at room temperature until double in size for the first rising (about 6-8 hours).

Cut the sweet potatoes into cubes and boil. (Or microwave until soft).

If the dough does not bounce back when you push your finger in, the rising is finished. It will rise to about 2x the original size. Depending on the temperature, the amount of time it takes to rise will change. It can also be done in the microwave by using the bread proofing function if you're in a rush. Just check on the dough occasionally and once it doubles in size, it's finished.

Use a scraper to divide into 8 sections.

Roll each section into small balls and let the dough sit for 15 minutes. Sandwich between two layers of damp cloth to prevent the dough from drying out.

Flatten out the dough, place the cooked sweet potato in the centers, and wrap the dough around it. Place the filled rolls the seam side down. Cover a baking sheet with parchment paper and place the dough on it for the second rising (about 60 minutes).

Cut open the tops with kitchen scissors so that the potatoes can be seen.

Put some pieces of butter into the cut tops and bake in a 200°C oven for 20 minutes.