Crumble the yeast and dissolve in 600 ml of lukewarm water. Knead in a large bowl with flour, salt and sugar with the dough hooks of the mixer to a smooth dough. Cover the dough and let it rise in a warm place for about 45 minutes until it has doubled in volume.
Line a baking tray (approx. 35 x 40 cm) with baking paper. Knead the dough briefly on a little flour and roll out to the size of the baking tray. Put it on the baking tray, cover and let it rise again for about 20 minutes.
Wash the rosemary, remove the needles and chop. Press hollows into the dough with your fingers close together. Sprinkle with rosemary and sea salt and sprinkle with oil. Bake in a preheated oven (electric cooker: 225 °C/circulating air: 200 °C/gas: see manufacturer) for 20-25 minutes until golden brown. Leave to cool.