For the tapenade, take all the ingredients apart from the oil and blend until smooth. Season with salt and pepper then add the oil. You may require more oil, especially if you are refrigerating the tapenade, but the texture should be quite thick.
For the celeriac remoulade, finely slice the celeriac and shred as finely as possible with a sharp knife. Stir in the mayonnaise, mustard and lemon juice. Season lightly. Cover and refrigerate until required.
For the salsa, remove the stems from the cherry tomatoes and cut through the centre of each tomato. Next, halve the sun-blushed tomatoes and mix both types of tomato with the shallot. Season and add the olive oil. Leave to marinate and add the torn basil leaves just before serving.
For the fish, take a heavy based frying pan and place on the heat. Make sure it’s hot before you add the oil, then heat the oil for a couple of seconds and add the fish, skin side down. It is really important you leave the fish long enough to let the natural sugars form a skin. When you start to see a golden brown edge around the fish, gently turn it and allow the pan to cool slightly. Then add the butter and a squeeze of lemon and remove to a warm area to rest for a minute or so.
To serve, place a round mousse ring on a room-temperature flat plate and spoon in your remoulade, leave for a few seconds to settle, then remove the ring. Place the warm fish on top. Next, place a helping of the tapenade on top of the fish. Spoon some chunky tomato salsa around the plate and finally drizzle a couple of tablespoons of the leftover tapenade oil around.