For the cure, put the salt, sugar and rosemary into a food processor and blitz for 3 minutes. Lay the Llampuga fillets on a tray and sprinkle evenly with the salt and sugar mixture. Turn the fish over a few times to ensure it is coated all over. Wrap the whole tray in cling film and place in the fridge to cure for 3 hours.
When the time is up, unwrap the fish and wash off the salt with cold water, then pat dry with kitchen paper. Wrap the fish tightly in fresh cling film and place back in the fridge for an hour to firm up.
To make the dressing, add the olive oil to a bowl and whisk in the verjus. Season with salt and pepper. To finish, slice the LLampuga as thinly and evenly as possible and lay it equally on 4 plates. Spoon the dressing over the fish, sharing the grapes and capers evenly. Scatter with chopped chives and pumpkin seeds, and then serve immediately.