The thing that I, as an newish maker, continue to find perplexing, is how the temperature varies so dramatically in the pot when I'm trying to cook it slowly over direct heat. I think that sometimes my probe must be in a curd, reading 30 C , while a minute later , in the whey near the bottom, its at 40. Constant stirring from the bottom, at least to begin, is what I remind myself; and the double boiler approach is even safer.