Combine the sourdough starter, water, 1/4 cup olive oil, honey, and salt in the bowl of a stand mixer with a dough hook.
Add the flour a half cup at a time until it starts pulling away from the sides of the bowl.
With your mixer on low to medium speed, knead until smooth and elastic. This could take anywhere from 10 to 40 minutes.
It should pass the windowpane test. Grab a small piece of dough and stretch it into a square. If it can stretch thin enough to see through without breaking, the dough is ready.
Place dough in a greased bowl and cover with plastic wrap or a tea towel. Let it ferment at room temperature until it is bubbly/puffy and has increased by about half the volume. The time this takes can vary on many factors, especially temperature and time of year. This could take 4 hours if left in a warm place. I sometimes let it go 8 to 12 hours. Be careful not to over ferment the dough.*
Put 1/4 cup olive oil in the bottom of a 9 by 13 baking dish lined with parchment paper.
Press dough out in the baking dish, pressing fingers down in the dough carefully. Be careful not to deflate it, and press it all the way to the edges.
Cover the dough in the baking dish with a tea towel or plastic wrap and allow it to rise for 1 to 2 hours at room temperature. It won’t double in size, but should become puffy and fill out the pan.
Drizzle with a few tablespoons of olive oil and sprinkle with garlic powder and chopped rosemary.
Bake at 425 degrees for 20 to 25 minutes or until it is golden brown.
Notes
Make sure not to over-ferment the dough. You will know if your dough is over fermented if it becomes a wet sloppy mess. It will be unworkable, and you won’t be able to shape it. If the dough over ferments, you can still bake it, and then turn it into sourdough breadcrumbs or sourdough croutons.
The amount of flour you’ll need will depend on the moisture level of your starter. If your starter is pretty runny, you may need more flour for the best results.
The dough can be quite sticky, so it may be helpful to dab your fingers in oil or use wet hands to spread the dough into the baking pan.
If you do not have a stand mixer you can also use the stretch and fold method. While the dough is in the bowl, grab the edge of the dough and pull up gently shaking the dough a bit while stretching it upwards. Then place the dough back in into the center of the dough. Turn the bowl a quarter turn and do this stretch and fold again, and again one to two more times. First 3 rounds of stretch and folds – every 15 minutes. Last 3 rounds of stretch and folds – every 30 minutes. Then cover and bulk rise.