Put the chickpea flour and 2 tbsp olive oil in a bowl. Roughly chopped half the rosemary leaves and add to the bowl, along with 2 tbsp parmesan. Add 300ml cold water and whisk until you have a smooth, thin batter. Set aside and leave to rest for 20 minutes.
Preheat the oven to 240°C/fan 220°C/gas mark 9. Heat 1 tbsp oil in a 20cm skillet pan until it’s smoking hot. Pour in half the batter and leave on the hob for 1 minute, until it starts to bubble like a pancake. Sprinkle over 2 tbsp parmesan and half the remaining rosemary. Transfer to the oven and bake for 10 minutes, until the farinata is golden and cooked and the edges are crispy. Transfer to a plate and keep warm. Repeat with the remaining batter. Cut each farinata into 8 triangles to serve.