Add milk, water and butter in a small pot and heat on medium low heat, until butter is melt. Mix the liquid well and set aside for 5 minutes.

Add 300 grams bread flour, dry yeast, sugar into a large bowl, mix well with a spatula. Add all the liquid from step one, eggs and salt into flour mix, mix by electric mixer on low speed (or by a spatula), until the liquid is cooperated with flour. Gradually add the remaining flour, 2 tablespoons at a time, and continue to mix by low speed (or knead the dough by hand), until the dough clears the side of the bowl but still a bit stick to the bottom of the bowl. If the dough doesn't come off the bowl, add in more flour and keep knead. If the dough is too dry, add in a teaspoon of water. The whole process might take 15 - 20 minutes or longer. The finished dough should be elastic and spongy. Cover the dough with a clean wet kitchen cloth or plastic wrap, and let it rest for 1 to 2 hours, until the size of dough doubled.

Line baking tray with parchment sheet, brush a thin layer of vegetable oil, set aside. Dust a big cutting board with flour and dust both hands with flour. Take the dough out and place on cutting board. Knead the dough a few more times, divide equally into 8 pieces by knife. Shape the dough into ball (or other shape you prefer) by hands, place on parchment sheet and slightly press it. (*see footnote) Cover the baking tray with plastic wrap and let the dough rise for another half to 1 hour.

While dough is rising, preheat oven to 200 degrees C (400 F). Gently brush egg white on the dough by fingers, sprinkle with black sesame seeds. Bake for around 10 minutes, until the bun turns golden brown. Chill down the burger bun a bit before serve.