Demonstrated at the 2011 Melbourne Food and Wine Festival.
Preheat the oven to 230°C.
Brush the inside of a small Swiss roll tin or roasting tray generously with olive oil. Sieve the dry ingredients, and make a well in the centre. Pour most of the buttermilk in at once. Using one hand, shaped like a claw, mix in the flour from the sides of the bowl, adding more butter milk if necessary. The dough should be softish, but not too wet and sticky.
When it all comes together, turn dough out onto a floured board and roll it out so that it fits into the Swiss roll tin. Use the tips of your fingers to create dimples in the dough’s surface, to make little wells for the olive oil. Place the 12 red onion chunks on the raw dough, (3 across and 4 down, so that there are 12 altogether) so each square will have some of everything. Next to the red onion place a pitted olive (press it down slightly) and a little sprig of rosemary, drizzle generously with olive oil and sprinkle with sea salt.
Bake in a hot oven 230°C for about 30 minutes or until cooked. When cooked, the bread should be nice and golden on both top and bottom.
If the bread gets a good golden colour and you don’t want it to darken any more while cooking, turn the oven down to 200°C and continue cooking.
When the focaccia is cooked but still hot, drizzle just a little more olive oil over the top. Allow to cool slightly before serving.