In a large mixing bowl or stand mixer, combine warm water, egg, sugar, salt, and yeast. Whisk for 1 minute to hydrate the yeast.

Add softened butter and most of the flour. Mix using a dough hook until the dough comes together. If sticky or dry, add a little more flour or water at a time until the right consistency is achieved.

Knead for 5-6 minutes until smooth and elastic.

Cover the dough with plastic wrap and let it rest in a warm place for about 90 minutes, or until it doubles in size.

Turn the dough onto a clean surface, divide into 8 pieces, and roll each into a smooth ball.

Place on a baking sheet, flatten slightly, and cover loosely. Let rise until puffed, about 60-90 minutes.

Preheat oven to 400°F. Make an egg wash by beating the egg with water, brush over the buns, and sprinkle with sesame seeds.

Bake for 15 minutes until golden brown.