Mix the toppings together in a small bowl and set aside.
Mix the yeast in 1/2 cup of warm water and set aside to froth for five minutes.
After five minutes, add the sour dough to a large bowl. Then add the flour, oil, and the remaining water and mix with a wooden spoon until everything comes together. This is a very sticky dough at this stage, but it's fine. That's what will make it divinely airy and light.
Cover the dough with plastic wrap and place in an oven with the pilot light on, about 1.5 hours or until it has doubled in size.
Using an oiled spatula, turn the dough over on itself in the bowl. Repeat 9 more times. You don't want to knead the dough with a heavy hand.
Turn the dough over on a generously floured surface. Cut into two with a bench scraper or a knife, then shape each half into a round. Be gentle so you don't deflate all the lovely gases that have formed in your focaccia loaf.
Place each round in a 10-inch cake pan coated with oil and sprinkled with some coarse sea salt. Press the dough gently out from the centre so it reaches the sides of the pan.
Cover both 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 sage-olive oil mixture topping. Bake in the preheated oven for 25 minutes.
Remove the focaccia tins from the oven and let them stand on a rack for five minutes. Remove the bread from the pans and continue to cool on the rack.