Method

Sift the flour and salt together on a cold work surface. Scatter the butter over and mix roughly. Form a well in the centre and add the iced water, mixing with a pastry scraper until a dough forms. Cover with plastic wrap and refrigerate for 20 minutes.

Roll the pastry out into a rectangle on a lightly floured surface, to a thickness of about 1.5 cm, and fold the short ends over to meet in the centre. Fold again, in half, in the same direction, then cover with plastic wrap and refrigerate for another 20 minutes. Repeat this rolling and resting process twice more.

In the meanwhile, heat the oil in a large saucepan and add the onions and thyme. Reduce the heat to low and cook, stirring occasionally, for 40 minutes. The onions must be soft but not browned.

Preheat the oven to 180 °C. Line a baking tray with baking paper.

Roll out the pastry to a size of 18 x 30 cm and a thickness of about 7 mm. Place the pastry in the baking tray. Drain the onions as much as possible, retaining the oil, and spread the mixture over the pastry. Drain the anchovies and make a lattice pattern on top of the onions with them. Drizzle with a little of the drained oiland place in the oven. Bake for 30–40 minutes until puffed and golden brown.

Remove from the oven and place a caper berry in each diamond shape. Serve hot.

Tip: It is a good idea to retain the drained oil from the onions and to use it again in other dishes as it has a wonderfully beguiling onion and thyme flavour.