This would not be a very useful blog if I only told you about the successes.
What happens if we sweeten and jar some yogurt and cook it in a pot of simmering water the way you cook sweetened condensed milk to make dulce de leche?
Well, nothing worth repeating, that's what. It took a long time for the sugar to caramelize -- I suppose I didn't sweeten it as MUCH as sweetened condensed milk -- and the yogurt became unpleasantly grainy and dry.
I should skim through McGee to see if there's a solution: at what temperature will yogurt do that, and is it a higher temperature than the temperature at which sugar caramelizes? Maybe it could be cooked longer at a sub-boiling temperature, in other words. I suspect not, but I feel compelled to speculate.