Add yoghurt, soft butter, sugar and salt and mix it together.
Add the flour and knead the dough. Add a little more flour if the dough is too sticky.
Make dough pieces of 90 grams (3.2 oz), shape them to 'normal' buns and let them rest for 5 minutes.
Use your hand to flatten them so that they have a thickness of about 2 cm (~1 inch). During baking they will expand into normal burger bun sizes. Cover a baking tray with baking paper and put on the buns.
Use a small pastry brush to cover the buns with an egg/water mix and sprinkle the buns with sesame. The egg/water mix will add a nice light-brown color to the buns and make sure the sesame stays on the buns.
Cover the entire baking tray with a plastic bag/plastic foil and with a kitchen towel. Put the buns a nice and warm place for about an hour. This step is important to make sure the buns become soft and delicious. The plastic bag will keep the moist inside the buns and the kitchen towel will keep them warm during the resting period.
Bake the buns at 230 C (450 F) for about 10-12 minutes.
Notes
If you want your buns to have a nice and even layer of sesame you can use this trick. Pour out sesame on a plate. Cover the top of the buns with the egg/water mix. Gently put the buns on the plate and give them a light press. Put the buns back on the baking tray.