Combine the flour, yeast, salt and sugar in a large mixing bowl or the bowl of a stand mixer. Add half of the oil and 250ml of warm water and stir to combine. The dough should be soft and sticky. If it is at all dry, add up to 50ml more water.

If kneading by hand, turn the dough out onto a lightly floured or oiled surface and knead gently for 5 minutes, return to the bowl, cover with a clean cloth and refrigerate for 1 hour. If kneading with a dough hook, knead 5 minutes, then cover and chill for 1 hour.

When the dough has risen, oil an oven tray with 1 Tbsp of the remaining oil. Turn out the dough onto the tray and stretch into a large rectangle, turning to coat in the oil. Cover again with a cloth and leave to rise for a further 30 minutes.

Meanwhile, heat the oven to 220°C / 425°F / Gas 7. When the dough has risen, mix the remaining olive oil with a tablespoon of water and drizzle over the bread. Use your fingers to press dimples all over the dough, then push the tomatoes, cut side up, and rosemary into the focaccia. Sprinkle generously with sea salt flakes.

Bake in the preheated oven for 20-25 minutes until puffed and golden. Drizzle over remaining tablespoon of olive oil while the bread is still hot. Allow the focaccia to cool for at least 10 minutes before slicing and serving.