Zest and juice the lemon, cutting the zest smaller. See our lemon Tip. Chop the parsley. See our herb Tip. Set aside for later. Drain the tuna in a sieve or colander, and add to the bowl of your blender or food processor. Add the anchovies, a few fillets or to taste. Add at least 1 tablespoon of capers, or more if liked. Add the lemon zest, plus a little of the juice and a good grind of black pepper. Add half the chopped parsley. Blend, ideally on the pulse setting, until well combined.
Add 1 heaped tablespoon of yoghurt or mayonnaise to the mix, blend well and scrape down the bowl to catch any stray ingredients. Continue adding and blending spoon by spoon until a smooth, pourable consistency is reached, but the sauce still has some body. Add a splash of hot sauce, if using.
Taste and adjust, adding lemon, pepper, capers, hot sauce, more anchovies etc until you get the flavour you like. It should be tangy, but still rich and savoury, and you should still be able to distinctly taste the tuna.
Pour the sauce into a bowl and chill in the fridge to develop the flavour, ideally for at least one hour. Remove from the fridge about 30/40 minutes before serving so the cold does not deaden the flavours.
Slice the tomatoes quite thickly, and arrange on a large plate or serving platter. A serrated knife makes this easier. Spoon over the room temperature sauce. Decorate with the remainder of the chopped parsley and a few more capers. Top with some basil, ripping the leaves as you add.
Serve with lots of crusty bread to mop up the delicious, moreish sauce.
Enjoy!
