1. Preheat your oven to 350 F (175 C). Line two large baking sheets with parchment paper.

2. In a medium-sized mixing bowl, combine the unfed sourdough starter, all-purpose flour, 1/4 cup olive oil, and 1/2 teaspoon fine sea salt. Mix everything together with a spoon or spatula until a shaggy dough forms. It will be slightly sticky.

3. Turn the dough out onto a lightly floured surface. Knead for just 1-2 minutes until the dough comes together and is smooth enough to roll out. Avoid over-kneading, as this can make the crackers tough.

4. Divide the dough in half. On a piece of parchment paper or a lightly floured surface, roll out one half of the dough as thinly as possible, aiming for about 1/16 to 1/8 inch thickness. The thinner you roll it, the crispier your crackers will be.

5. Use a pizza cutter or a sharp knife to cut the dough into desired shapes – squares, rectangles, or even triangles work well. Carefully transfer the cut dough pieces to the prepared baking sheets, leaving a little space between each cracker. Repeat with the second half of the dough.

6. Lightly brush the tops of the crackers with additional olive oil. Sprinkle generously with extra fine sea salt and any other desired toppings like sesame seeds or dried herbs.

7. Bake for 20-25 minutes, rotating the baking sheets halfway through, until the crackers are golden brown and crisp. Keep a close eye on them, as thin crackers can burn quickly.

8. Remove the baking sheets from the oven and let the crackers cool completely on the baking sheets. They will crisp up further as they cool.