First make the starter. Whisk together the starter ingredients, cover and leave for about 6-8 hours before using.
If you have kept the Poolish in the fridge, remove it and leave to warm to room temperature for 1 hour. Put the flour into a large bowl, make a well in the centre and add the Poolish, water, sea salt, yeast and olive oil, whisk and then combine everything with your hand to give a soft stretchy dough. Note- hold back some of the water- you may need less or a little more depending on the flour- that’s a rule for all breads.
Leave the dough for 5 minutes. Oil your work surface and hands. Using a dough scraper, remove the dough onto the surface. Pick it up with oiled hands and throw it forward into your surface keeping hold of one end so it extends and elongates on contact with the surface. Fold back towards you and repeat this process for 5 minutes until the dough is smooth and firmer. Have patience, you may need to use your dough scraper to help initially. Place on an oiled sheet and cover with cling film.
Let the dough rest for 1.5 hours, then tip it onto your oiled surface and gently flatten it slightly. Fold one end to the middle and the other end over the top- like puff pastry. Seal the ends, turn so one end is nearest to you and press it our using your finger tips, making dimples along the rectangle. Place back on the oiled baking sheet, cover and leave for another 30 minutes.
Repeat the pressing out and folding. Place back on the baking sheet again and use your fingers to create an even dimpled finish on the dough. Brush the surface of the dough with olive oil, followed by the cooked red onion, fresh chopped rosemary, Parmesan and a sprinkle of sea salt. Cover and rest for 30 minutes.
Bake in a pre-heated oven at gas mark 7 /220C / 450°F for 20-25 minutes. Rotate the bread 180° after the first 10 minutes to ensure even baking. Remove from the oven and the using a palette knife, remove the focaccia onto a cooling rack immediately. Cool for at least 20 minutes before cutting into slices.
