In a bowl, mix flour, dry yeast, sugar, salt and warm water and stir them well.
After 10 minutes, melt the butter and then let it cool down aside and then stir it into the bowl and knead them well. Close the bowl top with a moisturized piece of cloth or towel and let dough rest about 40 minutes.
After the dough rest, put some flour to counter surface and divide the dough to 6 equal pieces. Take the first piece of the dough you divide and roll it until it has 3-4 mm thickness (make very thin) and 18-20 cm radius with rolling pin. Apply the method to the remaining dough pieces.
Preheat the oven 250 C (482 F). Grease the oven tray with a little olive oil and place the first 3 pieces of Lavash.
Coat the tops of the dough disks with egg yolk and add the sesame seeds on top them. And then place the tray into the oven. Bake them about 10 minutes until the dough puff up high and began to change its color to light brownish.
Tip: If you have time, make them one by one and place the dough to the center of the tray to have best baking result.