Combine water and sugar and sprinkle the yeast on top. Leave for 10 minutes until the yeast starts to froth.
Add 1½ cups of the flour (sifted) into the yeast mixture along with the salt and olive oil. Mix well for about 3 minutes until the mixture is a silky texture. Gradually add the remaining flour and mix until incorporated.
Knead the dough, either on a lightly floured board by hand or in a stand mixer with the dough hook attachment for 10 minutes, until the dough is soft and elastic. The dough should spring back when lightly pressed.
Lightly oil a bowl and roll the ball of dough to coat. Cover with a tea towel that has been dampened with warm water and leave in a warm place until doubled in size. This usually takes around 1½ hours.
Remove from the bowl, knock the dough back using a fist and shape it into a round. Cover the bottom of a 10 inch round cake tin with olive oil (3-4mm) and place the dough into the tin. Spread the dough out so that it reaches the edges of the tin.
Using your fingertips make indentations into the top of the loaf and drizzle with olive oil. Sprinkle sea salt and rosemary, or any other topping choice and cover again with the re-dampened tea towel. Leave in a warm place for 30 minutes (on top of the oven is fine). Preheat the oven to 200°C.
Bake for 25-40 minutes (depending on thickness of loaf) until the top is golden brown and crisp. Remove from oven and serve immediately.
Focaccia bread is best eaten on the day it is baked, but stored in an airtight container it will keep for a couple of days...if it is not eaten before then!