It just seems to me that evaporation is a bug and not a feature. I don’t see how it’s possible without elaborate measures to simultaneously control evaporation and the the degree of cooking.
The rate of evaporation will vary not just with temperature, but with the size and shape of the vessel, the quantity of mix, the rate and type of stirring, and the ambient temperature and humidity.
So if you’re cooking to a set time/temperature, the evaporation will vary. If you cook to a set evaporation (by stopping and measuring frequently?) the cooking time will vary.
If you want to increase milk solids, add nonfat dry milk. There are zero downsides. Use a good brand and it will be pure skim milk, spray-dried at a lower and better controlled temperature than what you’ll ever manage in the kitchen. There’s a reason that most of the best pastry chefs do it this way.
If I didn’t do sous-vide, my first choice would probably be a lab hotplate, with a pan lid drilled for the thermocouple probe.
Edited to add: 1° accuracy should be more than good enough for ice cream. Is there a way to cover the KA heated bowl while it's working?
