Bring the water to a boil in your large pan. Add the rice, water, salt, and butter. Then you can add the milk.
Let it boil, then lower the temperature to medium heat. Let the water absorb into the rice so it thickens up a bit, this takes about 5 minutes.
Let your porridge simmer on medium-to low heat for around 40-45 minutes so that the consistency thickens up and the rice feels soft when eaten.
Serve with cinnamon, sugar, and milk. Also, plum- or fruit soups are traditional additions.
Notes
If you use a double boiler pan set with water in the bottom pan it might take a longer time to cook your porridge. Plant-based milk is an option for a milk-free, vegan porridge. Replace butter with margarine or leave it out. Store leftovers in fridge and reheat in pan adding some milk to it since it thickens a lot when cooled down.