75ml extra-virgin olive oil plus more for brushing
Preheat the oven to 220C. Stir together the flour, chopped rosemary, bicarbonate of soda and salt in a medium bowl. Make a well in the center, then add the water and oil and gradually stir into the flour with a wooden spoon until the dough takes form. Knead it gently on a work surface 4 or 5 times.
Divide the dough into 3 pieces, cover 2 of them with clingfilm and roll out the other on a sheet of baking paper into a 25cm round (the dough should be thin).
Lightly brush the top with additional oil and scatter small clusters of rosemary on top, pressing in slightly. Sprinkle with sea salt. Bake on a preheated oven tray until pale golden and browned in spots – about 8-10 minutes. Transfer the flatbread to a rack to cool, then repeat with the other more rounds.
Flatbreads can be made 2 days ahead and cooled completely, then storage in an airtight container at room temperature.