Crumble the yeast and dissolve in 600 ml of lukewarm water while stirring. Put salt, flour and sugar in a large bowl. Add yeast water and knead everything into a smooth dough. This is best done with a food processor or by hand.
Cover the bowl with a damp tea towel. Let the dough rise in a warm place for about 45 minutes until it has doubled in volume.
Line a baking tray (approx. 32 x 39 cm) with baking paper. Knead the dough briefly on a floured work surface. Roll out to the size of the baking tray and place on the tray. Cover and let rise again for about 20 minutes.
Wash the rosemary and shake dry. Remove needles and chop. Press hollows into the dough with your fingers close together. Sprinkle with rosemary and sea salt and sprinkle with olive oil. In a preheated oven (electric cooker: 225 °C/ convection oven: 200 °C/ gas: see
manufacturer) Bake for 20-25 minutes until golden brown. Remove and let cool on a cake rack.