Crumble yeast in 1⁄4 l warm water and dissolve while stirring. Put 500 g flour, 1 teaspoon salt and 1 pinch of sugar in a bowl. Add yeast water and 4 tablespoons of oil. Use the dough hooks of the mixer to knead into a smooth dough that comes off the bowl rim.
Then continue kneading for about 3 minutes. Cover the dough and leave to rise in a warm place for about 1 hour until its volume has almost doubled.
Wash the rosemary, shake dry and remove the needles. Coat a baking tray (approx. 35 x 40 cm) with oil and dust with flour. Knead the dough again briefly. Roll out on the baking tray to a large flat cake.
With floured fingers, press in depressions at even intervals. Sprinkle with 4-6 tablespoons of oil. Sprinkle with sea salt and rosemary. Cover and leave in a warm place for another 45 minutes.
Preheat the oven (electric cooker: 225 °C/circulating air: 200 °C/gas: see manufacturer). Bake Focaccia in the hot oven for about 20 minutes.