Rupees are kinda hard to come by in this game surprisingly, but apples aren't. So I've been taking up all my excess apples and cooking them together to sell back (from 3RPA to 10RPA cooked). There was one time while cooking Simmered Fruit (5 apples), the music played back was slightly different and I managed to cook a "special" Simmered Fruit.
It's "special" in that it looks exactly the same as the regular Simmered Fruit dish and has no distinctive look or description (and costs the same) but it heals 8 hearts rather than the usual 5.
How often can I expect this to happen?