I view this as an example of rather impressionistic writing. English words are being used in unusual ways, in some cases drawing on technical meanings from the world of whisky appreciation.
I'm not completely sure what author means by outrageous, but from context I deduce that it's implying "unconventional, but very enjoyable." The phrase
so bad it's good
comes to mind. "Bad" in this case could be due to the very idea of re-distilling expensive whisky, or the resulting price of the sorbet, or simply that this is a surprising but welcome experience.
Initially I thought that the idea of re-distilling whisky would be a bad thing, but it does seem that some connoisseurs experiment with modifying whisky flavours in this way. The general effect seems to be that the volatile alcoholic portion of the whisky separates off giving a lighter flavour, with much of the original flavour left behind. It is that "left-behind", flavourful, portion that is being used to make the sorbet.
When one eats the sorbet, the melting reveals the old whisky flavour. The writer is using a metaphor of "aging" to describe that experience. Remember that whisky gains its flavour and colour from aging in oak barrels for a period of years.
Obviously the whisky portion of the sorbet is not aging as you eat it, however the flavours are revealed as the sorbet melts, the aging becomes apparent.