Mix sugar, milk, and lukewarm water. Add fresh yeast and let it dissolve. Combine flour, egg, soft butter, salt, and squid ink. Mix well and let the dough rise.
Shape the dough into buns and let them rise again. Brush with egg yolk and milk mixture. Sprinkle black sesame seeds on top.
Bake the buns in a preheated oven at 350°F (175°C) for about 20 minutes or until done.