Preheat the oven to 200℃. Add the flour to a food processor with a good pinch of flaky salt. With the machine running, add enough sourdough to form a supple dough that's not sticky (about 200g, but this depends on your flour). Knead for 10 minutes until smooth, soft and a little shiny. Cover and rest for an hour.
Roll out the dough as thinly as possible. I think the best tool for this is a pasta machine (full technique tutorial here), but you can use a rolling pin if you don't have one.
You can bake the sheets whole and break them up after cooling or cut the dough sheets into circles with a pastry cutter. Brush with a little water (don't go overboard) and sprinkle with the crushed peppercorns. Bake for about 5 minutes, until completely dried out, very crunchy and lightly browned. Cool to room temperature (this should only take about 10 minutes).
Any leftovers can be stored in an airtight container.