Line a deep bowl with a cheesecloth or muslin. Stir the two yoghurts together with ½ a teaspoon of salt and pour into the cloth. Bring the edges together, form a tight bundle and tie firmly with a string. Hang the bundle over a bowl or from your tap over the kitchen sink. Leave the yoghurt to drain for 24-36 hours. After this time much of the liquid should have been lost and the yoghurt will turn thick and quite dry; the centre may still be creamy. Next, remove the labneh from the cloth and spread onto a large plate. For the topping, dice the olives and place them in a bowl with the oregano, parsley, preserved lemon, garlic and olive oil, reserving 2 tablespoons of oil for the tomatoes. Use a pestle and mortar to crush the nuts unevenly, leaving some just broken and others finely crushed. Add to the olive mix and stir together. Spoon the olive mix over the labneh and sprinkle with chilli. Finally, cut the tomatoes into thick wedges and mix with the onion. Arrange in a pile in the middle, sprinkle the sliced onions over and then finish with olive oil and sea salt.
