Combine all the ingredients in a bowl. Let the dough sit for 10 to 20 minutes to absorb the moisture and firm up.
Divide the dough in half.
Place one piece of dough onto a piece of parchment paper and roll it out into a thin rectangle. It should be about 1/16 inch thick.
Slide the sheet of dough onto a baking sheet. Brush the top with olive oil and sprinkle with grated parmesan, salt, and pepper.
Repeat with the second piece of dough.
Bake for 28 to 30 minutes. (Thicker crackers will need to bake longer)
Remove from the oven and let cool. Once cool, break into small cracker-sized pieces.
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Notes
Starter or discard: You can use either active (fed) sourdough starter or sourdough discard. Discard will give the crackers a more pronounced tang.Baking time: It depends on how thin you roll the dough. Start checking around 20 minutes and use the color as your guide. Golden edges mean crisp, dark brown means overdone.