All it takes is a quart of buttermilk and a gallon of milk.
Put them in a large heavy bottomed pot and cook on high. The solids will separate around 190 degrees, (I don't use a thermometer).
Once it separates, you just strain the solids into a cheese cloth or thin dish towel and squeeze the water out.
You can use it immediately or put in the fridge for a few days.
I have to say, if you make this at home, you might as well use organic milk, and use at least 2% so you get a little fat in it. I did use fat free once and it was good, but I got a lot less of it.