Put the yeast and sugar in 1 cup warm milk and wait 15 min. for it to bubble.
In a separate bowl, beat 1 whole egg with the white of the other one and add the pre-melted butter.
Subsequently, add the oil, effervescent milk, salt and flour, then knead a smooth, nonstick dough.
Smear the well-formed buns with pre-beated egg yolk on top and put them in a 392°F (200 °C) oven.
It's recommended to put them on top of baking paper. They'll be ready in about half an hour.