1tablespoonfinely chopped fresh rosemary(plus two additional sprigs)
1/3cupolive oil,plus more for brushing
flaky sea salt
Preheat the oven to 450°F with a heavy baking sheet on rack in middle.
In a medium bowl, stir together the flour, chopped rosemary, baking powder, and salt. Make a well in center, then add the water and oil and gradually stir into the flour mixture with a wooden spoon until a dough forms. Knead the dough gently on a work surface 4 or 5 times.
Divide the dough into 3 pieces and roll out 1 piece (keep the remaining pieces covered with plastic wrap) on a sheet of parchment paper into a 10-inch round (shape can be rustic; dough should be very thin).
Lightly brush the top of the dough with additional oil and scatter small clusters of rosemary leaves on top, pressing in slightly. Sprinkle with sea salt. Slide the round (still on parchment) onto the preheated baking sheet and bake until pale golden and browned in spots, 8 to 10 minutes. Transfer the flatbread (discard parchment) to a rack to cool, then make 2 more rounds (1 at a time) on fresh parchment (do not oil or salt until just before baking).
Break into pieces and serve.
Flatbread can be made 2 days ahead and cooled completely, then kept in an airtight container at room temperature.