Heat the milk until lukewarm. Make sure the temperature of the milk is not higher than 30 degrees Celsius or 86 degrees Fahrenheit. If the milk is too hot, this may result in de-activating the yeast.
Mix the yeast with the milk and let it rest for 5 minutes.
In another bowl, break the eggs. Use a fork to slightly whisk the eggs. In such way that the egg whites and egg yolks are blended.
Making the Dough
Add the flour, salt and sugar to the eggs. Mix through, whereafter you can add the milk and yeast mixture.
Slightly dust the kitchen counter with flour. Knead the brioche dough for about 10 minutes. Since the dough is very sticky and soft, you can just drop the dough on the kitchen counter. Repeat this until the dough doesn't stick to the counter anymore. You can use some more flour of course, but make sure not to add too much. This will make the bun less soft!
Grease the bowl with some olive oil and add the dough to it. Cover with a moist kitchen towel, and place the bowl on a warm place in the house. Let the dough rest for about 1 hour.
Continue with the dough..
After one hour, you can add the butter to the dough. The easiest way is to add the butter cube by cube. When all the butter is incorporated, the dough needs to rest for another 3 hours.
Let's make the buns!
Divide the dough in 6 even pieces and roll them into balls. Place a baking paper on the sheet pan. To make sure the buns don't stick to the paper, you can slight grease it with oil. Place the buns on the baking paper and cover again with the moist kitchen towel. Let them rest for 45 minutes.
Preheat the oven on 200 degrees Celsius or 392 degrees Fahrenheit.
Brush the buns with egg yolk and top with sesame seeds. Bake the buns in a preheated oven for about 12-15 minutes.