Mulberry Jam
I recently had the pleasure of sampling this quite fairly-hard-to-come-by jam, and I have to report that unfortunately it's god damn delicious. And not made from handbags.
Looking rather like a blackberry or raspberry, the mulberry was a Jacobean fashion when it came to the UK and trees can still be found in the gardens of some stately homes, including Chastleton House in Oxfordshire and Charlecote Park, Warwickshire, where there is a receipt dated 1713 for the purchase and planting of a tree that is still flourishing.
The trees tend to grow fairly large and the fruit does not weather well after being harvested (they are quite soft and liable to explode when touched). This might have something to do with the commercial scarcity of the fruit and by extension the rarity of the jam shown opposite by Wilkin's. Nowadays the best way to get your tongue around this genuine rarity would probably to grow yourself a tree and make the stuff yourself.
If you do get chance to sample it, or spot it at a supermarket/farm shop then snap it up quick. They don't come around often. Enjoy with heart attack inducing pastry of choice. Very tasty.