To make the potato cakes, peel, cut and boil the potatoes in salted water for ten minutes and then mash with a little milk and salt and pepper until you reach a smooth consistency. Cover with a damp cloth to allow the mash potato to cool without drying out.
Pan fry the prawns with some olive oil and some salt until the translucency begins to disappear and then allow to cool, before chopping into small pieces.
Finely chop the leek (all the white and some of the firmer green part), wash with plenty of cool water to get rid of the dirt in between the layers and sauté with a little butter and season to taste with salt and pepper.
Mix all the ingredients together in a large bowl with the parsley and flour and mould into four flat round shapes. These cakes can be made in advance, cling filmed and stored in the fridge.
To make the chilli jam, de-seed and finely chop the chillis. Add to a sauce pan with the sugar and the vinegar, bring to the boil and then reduce heat and simmer for 15 minutes before allowing to cool to room temperature.
For the sautéed prawns, finely chop the garlic and fry in some olive oil together with the prawns kept whole until the vibrant pink and white colours come through and the prawns are no longer translucent.
For the tempura prawn, mix in a bowl the two types of flour and add the sparkling water bit by bit whilst whisking the mixture. The consistency of the batter should be thick enough to coat the wires of the whisk, but still runny so that it does not stick to the whisk. Season with salt.
Holding by the tail, dip each tiger prawn up to the tail into the batter and deep fry until the tempura batter turns golden.
To serve, pan fry the potato and prawn cakes in olive oil for one minute on each side to a pale golden colour and the whole cakes are warmed through.
Serve on a warmed plate with some watercress dressed with some olive oil, freshly squeezed lemon juice and salt with two garlic sautéed prawns and some chilli jam drizzled around the edge of the plate.