Mix brown sugar with flour and sesame seeds. Slightly crush to remove any bumps.
Add flour, salt, sugar, vegetable cooking oil and water in a large bowl. The dough should be kneaded for 8 to 10 minutes until very smooth in surface and becomes white (because we only knead once). Shape the dough into a long log and divide into 10 portions.
Place around 3/4 tablespoons of filling in center. Assemble the dough as triangle. Rest the buns in room temperature for 1 hour (20 degree C in room temperature) until they are 1.5 times in size and can recovery very quickly if you press the skin. In winter days, I love to place them in an oven with a plate of hot boiling water at the bottom. This can speed up the proofing in cold weather.
Set up the steamer with cold water and steam for 12 minutes. Then rest for another 5 minutes. Enjoy hot!