Adapted from my favorite yeasted, slow-rise focaccia recipe — overnight refrigerator focaccia — this recipe replaces the yeast with a sourdough starter. UPDATE: Video guidance is here! Watch up above or click the link below in the recipe card.  What you need to make this recipe...: ...a sourdough starter. I bought mine from Breadtopia. It was easy to activate. There are no instructions on the package itself; follow the instructions on the video here. ...time. Once your starter is ready to go, this recipe requires an initial 4- 18 hour rise, followed by a second 4- to 6-hour second rise. After the initial rise (depending on the time of year and temperature of your kitchen), you can deflate the dough, and stick it in the fridge for 8 to 10 hours (maybe longer), which might help you regarding your schedule. Keep in mind, when you remove the dough from the fridge and transfer it to a pan, it will still need to rise for another 5- to 6- hours. ...water. Apparently, chlorine in water can adversely affect sourdough. Leaving water at room temperature for 24 hours will allow most of the chlorine to escape.When I am in the habit of making sourdough bread, I fill a large pitcher with water and leave it out at room temperature. I use this for my sourdough breads and starter. Truth be told, I've used water straight from the tap and have not noticed a difference. Water quantity: Depending on where you live and the time of year, you may need to cut the water back. If you live in a humid environment, for instance, I would suggest starting with 430 g water. If you are not using bread flour, you also may need to cut the water back a bit. Timing: The more I make sourdough, the more I realize so much depends on the time of year and the temperature of my kitchen. In the summer, because it is so warm, the first rise (bulk fermentation) takes between 4 - 6 hours; in the winter the first rise takes 12 - 18 hours. The key with this recipe is to make sure the first rise doesn't go too long — you want the dough to nearly double. A straight sided vessel  (as opposed to a bowl) makes gauging the first rise easier. (Note: If your dough rises above double, don't despair ... recently my dough tripled in volume during an overnight rise, and the resulting focaccia was still delicious, light, airy, etc.) A few thoughts: If you are making this focaccia in the summer (northern hemisphere), use 50 g of starter and check the dough every couple of hours. If you are making this in the winter, use 100 g of starter, and plan for a long first rise. Troubleshooting: If you have issues with your dough being too sticky, please read this post: Why is my sourdough so sticky? The 4 common mistakes. Flour choice:  I've been using King Arthur Flour's special patent flour — bought a 50-lb. bag of it at Restaurant Depot. Its protein content, 12.7%, is the same as the protein content of its bread flour. I also have used all-purpose flour (11.7%) with success, but I recommend bread flour, which seems to be more reliable for people especially those living in humid climates. If you only have ap flour on hand, you may consider reducing the water a bit — bread flour absorbs slightly more liquid than all-purpose flour.