Combine the lukewarm water, sugar and yeast in a bowl and allow it to stand in a warm spot for a good 15 minutes to give the yeast time to activate and start bubbling. Now if you have a food mixer, things get super easy. Fit your mixer with its dough hook and, with the speed on low, mix together the flour, tablespoon of salt, half a cup of the olive oil and the yeast mixture. Once it starts coming together, let your mixer continue to knead it for 6 minutes. (You can do this by hand if you do not have a mixer, it’s just not the most pleasant kneading experience as this is a very tacky dough. But it still works.)
Tumble the dough onto a lightly floured surface and fold it over a few times. Then pop it into a large bowl lightly painted with olive oil, cover with cling film or a damp towel and leave to prove for an hour until it has doubled in size.
Pour the remaining half a cup of olive oil into a flat baking tray (the kind you would use to make a Swiss roll) and tumble the dough onto the tray. Use your hands to gently stretch it out to fill the pan then turn the dough over so both sides are well coated with oil. Use the tips of your fingers to push deep holes into the dough – this will create that lovely dimpled surface on the focaccia once baked – and set aside to prove for 40-60 minutes until it has doubled in size. Push rosemary into the focaccia and sprinkle generously with flaked Maldon salt. It is necessary to add this extra salt on top as the bread will be under-salted if you don’t. Bake in a pre-heated 220 degree Celsius oven for 25-30 minutes until it’s golden brown. Tuck in!