In a large bowl, whisk together the flour, salt, and instant yeast.
Add the olive oil and warm water.
Bring together until you have a wet sticky dough ball.
Knead briefly with oiled hands until it is smooth.
Brush with olive oil and leave in an oiled bowl with a damp tea towel over the top.
Leave to prove for 2 hours or until doubled in size.
Line your baking tray with baking paper then tip out the dough on top.
Oil your hands again and stretch it out into a large rectangle covering the baking tray.
Press dimples into the dough at random intervals.
Brush again with olive oil and cover.
Let it prove for another hour.
While the dough is proving slowly fry your onion slices in a pan on a low heat until just sticky.
Pre-heat the oven to 220 C / 425 F / gas mark 7.
Oil your hands and press down into the dimples again to make sure they are defined.
Sprinkle over the rosemary and salt flakes along with the onions.
Place in the centre of the oven and bake for 25 - 20 minutes until golden on top.
Transfer to a cooling wrack but it's best enjoyed while still warm!