I have never made such fluffy donuts!

What ingredients do I need for fluffy donuts?
Common wheat flour, 520 g.
Sugar, 75 g. A little more to coat the donuts.
Dry baker's yeast, 6 g.
Butter 50 g.
Whole milk, 150 ml.
Water, 100 ml.
1 egg L (weight between 55 - 60 g)
Salt, 4 g.
Oil to fry the donuts.