In a jug, add the yeast and sugar to the warm water and set it aside in a warm place. Wait for the yeast to react. (Approx. 20mins)
Put the flour in a mixer with a dough hook, and add the salt and yeast to it. Mix for approx 5 minutes. The dough should be soft but not sticky.
Gently oil the dough, cover and put to one side until it has doubled in size. (Approx. 1 hour)
Gently knock back the dough and knead in some olive oil. Oil a pan, and gently shape the dough to fit a rectangular baking pan.
Cover and leave to one side until the dough has doubled in size. (Approx 1 hour)
Sprinkle on some more olive oil and make dents in the surface of the dough using your finger.
Finely chop the rosemary and sprinkle it onto the top of the dough with a little sea salt.
Place into a pre-heated oven at 200 °C / 400 °F / Gas 6 and cook for approximately 20-25 minutes until golden brown.