The Flavor Apprentice RY4 Asian. This is a DIY flavoring but I haven't found anything else as good. I'm mixing at 8% and flavor is somewhat subtle, but with a thick mouthfeel and nice buttery finish. The analysis is interesting, it has fewer ingredients than many tobacco flavors or caramels alone. It's like it goes directly to the connection between caramel and tobacco flavors and avoids the middleman. The second best I've tried was Cigabuy's RY4 which is even cheaper than making your own, but while very similar (from memory) is a little too subtle and scares me a bit. The TFA flavor does contain acetoin up to 1%. I would tend to avoid vaping it at an 8% mix in vast quantities but then, like some other tobaccos, the flavor explodes in an EVOD and can be underwhelming in fruity juice eating machines.
Of other RY4s, I did some vape shop sampling of Tribeca, Gremlin's RY4, a Hangsen RY4 mix, and Coval's Azeroth and was underwhelmed to unimpressed. Could be good in better conditions. I have owned MyFreedomSmokes RY4 but it was a long time ago, decent. Mt. Baker's Ruyan 4 is a little strange but close.
Note there are 2 ways to DIY, one is to go nuts and start a new hobby, the other is get a flavor or 3 known to produce results in a simple one-flavor mix. The TFA RY4 Asian is definitely one of those.