This didn't quite come out how I intended, but I don't actually care, it is very, very good! Quantities for the peach bit are approximate - depends on how many peaches/how much yoghurt/etc, you have.
5 ripe peaches
3 tbs white sugar
About the same amount, or a little more, Greek yoghurt (depends how much you have!)
About 150 ml whipping cream
2 tbs peach liqueur (optional)
1 quantity butterscotch sauce using David Lebovitz' wonderful recipe (Please note that "heavy cream" is apparently whipping cream, not double).
Soak the peaches in boiling water for c 1 minute until the skins slip off easily. Remove them, the put the flesh in a large bowl. Blitz with a stick blender (or use a food processor) until you have a smooth puree. Now add the sugar, yoghurt, cream and liqueur, if using, and continue to blitz until well mixed. Chill thoroughly in the fridge, and freeze in ice-cream maker.
I meant to make the butterscotch sauce go through the ice-cream as a ripple, but either it wasn't quite cold enough, or the peach ice-cream wasn't quite as frozen as I'd thought, as it went a bit liquid, plus there was rather too much for the ice-cream maker. So I emptied most of the frozen peach into a freezer-proof bowl, and continued to work the ice-cream maker with the liquid remains; it didn't really freeze solid, but enough so I could add it in to the rest of the stuff. Of course we had quite a lot of tastes that night - but really, next day when I came to try it, it had turned into a sort of marbled-effect ice-cream, and was (and still is) seriously delicious! Not quite sure if it's reproducible, though!