In a bowl combine sugar, dry yeast and water and set a side for 10 minutes.

Sift flour in a large bowl, add salt, butter and yeast mixture.

Knead the dough for 10 minutes. Add more flour if needed. You can use a stand mixer with dough hook. Dough needs to be smooth, but sticky.

Transfer dough to an oiled bowl and cover with plastic wrap.

Let it rest in a warm place, until it doubles its size or for about 2 hours.

Heat oven to 425F and add a baking pan full of water to the lower back of oven. This will create more steam inside the oven and help the dough rise b=more quickly in the first 10 minutes of baking.

Line baking pans with parchment paper.

Divide dough into 12 portions and shape each one into a tight ball, using some more flour if needed.

Place bowls on baking sheet, leaving enough space between them.

Lightly brush balls with oil and egg yolk. Cover loosely with plastic wrap and let them rise for another 30 minutes.

Uncover dough and sprinkle each ball with sesame seeds.

Bake, rotating once until golden, or for about 20 minutes. Let them cool on a cooling rack.