For the pastry, place the flour, sugar and 1 teaspoon of sea salt in a food processor and blitz until combined.
Dice the butter and add half of it to the processor, then whiz for 30 seconds. Add the remaining butter and process for 1 minute. Add 100ml of cold water and pulse until large lumps form.
Transfer to a lightly floured surface and form into a rough dough. Gently knead with the heel of your hand for about 30 seconds, or until just combined.
Flatten to a disc, wrap in clingfilm and refrigerate for at least 1 hour.
Remove the dough from the fridge and roll out on a lightly floured surface to 5mm thick.
Lay the pastry over a 10cm x 35cm tart tin and carefully press into the base and sides. Trim the excess with a sharp knife, then line the case with 4 layers of clingfilm and chill in the fridge for 30 minutes.
Preheat the oven to 180ºC/gas 4.
To blind bake the pastry, fill with ceramic pastry weights, rice or beans and bake for 15 minutes. Lift out the weights using the clingfilm and bake for another 5 minutes, or until the base is dry. Set aside to cool in the tin.
To make the filling, peel and finely slice the onion and garlic. Peel, deseed and chop the plum tomatoes.
Heat 1 tablespoon of oil in a large pan over a medium heat. Add the onion and garlic and cook for 4 to 5 minutes, or until softened.
Add the tomatoes and tomato purée, pick in the thyme leaves, and cook for 20 minutes, or until the mixture has thickened, stirring occasionally. Remove from the heat and leave to cool.
Place the pastry case on an oven tray and spread the tomato mixture evenly over the base.
Crumble over the feta, scatter over the olives, top with the anchovies and drizzle with oil.
Bake the tart in the oven for 30 minutes, or until the top has caramelised slightly. Serve warm or cold with a green salad.
