Add yeast, warm water and sugar to a bowl. Let stand for 5-10 minutes, until foamy.
Whisk in egg and melted butter.
Mix in salt and flour, one cup at a time. Continue to add flour until you have a soft dough.
Knead by hand on a lightly floured surface for about 5minutes. Or knead in a mixer for 3-5 minutes until dough is smooth and elastic.
Do not let dough rise.
Divide dough into 8 equal pieces. Shape into balls.
Preheat oven to 425 degrees.
Place dough balls onto a baking sheet lined with parchment paper. Cover with towel and let rest for 10 minutes.
Mix together egg yolk and water (for the topping) and brush on top of the buns. Sprinkle with sesame seeds.
Bake for 8-10 minutes or until golden brown.