In a large, flat, stainless steel pan, make a dark caramel with the sugar
When smoking but not burned, add the balsamic vinegar and salt and let the vinegar reduce and dissolve the caramel making a gastrique (be warned it will spit a lot when the vinegar is first added)
When the gastrique is fully dissolved pour over the raspberries and refrigerate for minimum 8 hours or as long as 3 weeks
Spoon the raspberries over cheese or alongside pate. Combine the liquid with soda water for a tasty, not too sweet soda.