Place 500g strong white bread flour and either 7g fast-action dried yeast or 20g fresh baker's yeast in a large bowl. Add 400ml lukewarm water (about 35-40°C) and stir until just combined and no dry flour remains.
Cover the bowl with cling film or a damp tea towel and leave to rest for 15 minutes to allow the flour to absorb the water.
Add 10g fine salt and 50ml extra virgin olive oil. Knead the dough in the bowl by stretching and folding for about 5-7 minutes, until it feels elastic.
Lightly oil another clean bowl with extra virgin olive oil. Transfer the dough to it, turning to coat all over. Cover and set in a warm place for 1.5-2 hours, until it has doubled in size.
Oil a 30cm x 40cm baking tray with extra virgin olive oil. Tip the dough onto the tray without knocking out the air. Gently stretch it with your fingertips to fill the tray and create dimples across the surface.
Drizzle the surface with extra virgin olive oil. Scatter sprigs of fresh rosemary, pitted and halved black olives (e.g. Kalamata or Aragon) and halved cherry tomatoes over the top. Sprinkle with sea salt flakes. Leave to prove for 30-45 minutes, until puffed up.
Preheat the oven to 220°C (200°C fan/Gas mark 7). Bake the focaccia for 20-25 minutes, until the edges are golden and crisp.
Remove from the oven and drizzle with a little more extra virgin olive oil. Transfer to a wire rack and let cool slightly before slicing and serving.