When the water with groats boils, get rid of all the foam if there is any. Lower the heat so that water gets to constant simmering and cook porridge for 15-20 minutes until the water fully cooks off.
Pour milk into the pot with boiled groats, and thoroughly mix until ingredients fully combine. Since the groats are already cooked, our task now is to get the porridge of the consistency you want. After milk boils in the pot, I tend to cook porridge for 10 more additional minutes, of course constantly stirring (as I do not want to get burned porridge).
When you think that it is enough for boiling porridge in milk, turn off the stove, cover the pot with a lid, and set it aside. Let it rest for 5-10 minutes before serving.