Mix the toppings together in a small bowl and set aside.
Mix the yeast in ½ cup of water and set aside to froth for five minutes.
After five minutes, add the sourdough to a large bowl. Then add the flours, oil, and the remaining water and mix with a wooden spoon or in the bowl of a stand mixer until everything comes together. This is a very sticky dough at this stage, but that is what will make this focaccia light and airy.
Cover the dough with plastic wrap and place in an oven with the pilot light on or in a warm place for about 1 ½ hours or until it has doubled in size.
Using an oiled spatula, turn the dough over on itself in the bowl for a total of 10 times. You don't want to deflate the dough too much so don't knead it by hand.
Turn the dough over into a large baking pan (15 by 10 inches) sprinkled with some coarse salt. Or divide in half and place each half in a 9-inch cake tin. (I used a glass baking dish which wasn't such a good idea, because the baked bread was a bear to unmold. I'd advise using a metal pan)
Press the dough gently out from the center so it reaches the sides of the pan.
Cover the pan or pans with plastic wrap and place in the oven with the pilot on for another hour or until the dough has doubled.
Preheat your oven to 400 degrees at least 30 minutes before baking.
Using a fork, prick the dough all over to remove any bubbles on top. Don't go heavy-handed because you don't want to deflate the dough.
Brush the top of the bread with the rosemary-olive oil mixture. Bake in the preheated oven for 25 minutes.
Remove the focaccia pan or pans from the oven and let stand on a rack for five minutes. Remove the bread from the pan and continue to cool on the rack.