Preheat the grill to high.
For the sardines, remove the head from the sardines, then cut open along the belly from the head end to the tail and open out, flesh-side down. Press down along the body with the heel of your hand, then turn the fish over and lift out the bones. Make a slit next to the gills and tuck the tail into the slit, forming a circle.
Place the sardines onto a grill tray and season with salt and freshly ground black pepper. Place under the grill for 3-4 minutes, or until completely cooked through.
Meanwhile, for the pan-fried Jersey Royals, heat a frying pan until hot and add the potatoes and olive oil. Fry for 3-4 minutes until golden and crisp, then season with salt and freshly ground black pepper.
For the sauce vierge, place the extra virgin olive oil into a pan and whisk in the lemon juice. Add the tomatoes, shallot and garlic and place on the heat to just warm through. Remove from the heat, add the herbs and season with salt and freshly ground black pepper.
For the salad, place the salad leaves into a bowl, drizzle over the balsamic vinegar and the olive oil and stir.
To serve, divide the pan-fried potatoes among four plates and top each with three grilled sardines. Spoon over the warm sauce vierge and place the dressed salad leaves alongside.