Autolyse: Add the warm water and flour to the bowl of a stand mixer. Mix until incorporated using a dough hook. Then cover with a damp towel for 20 minutes.
Preheat the oven to 425°
Next, add the sourdough starter, olive oil, and dried rosemary to the bowl. Using the stand mixer again with a dough hook, mix all the ingredients together until it forms a ball. Usually, about 2-4 minutes of mixing.
Prep a work surface for rolling out dough. Flour your work surface. Cut the dough into approximately 1/2″ chunks. Then roll out each chunk into a super-thin, roundish shape using a rolling pin. You’ll want to continually flour the rolling pin so the dough doesn’t stick. This dough is easy to roll, think pizza dough. If you’re having trouble rolling out the dough, coat it in some flour and try again.
Transfer the flat dough to a silicone baking mat on a cookie sheet. Sprinkle with sea salt and pop it in the oven for about 12 minutes. If making a single batch, you’ll need two trays for all the crackers. You can bake them at the same time or one after the other.