In a large mixing bowl, combine the flour, grated Parmesan cheese, dried or chopped sage, salt, and pepper.
Add the sourdough discard, melted butter, and water to the dry mixture. Stir until a shaggy dough forms. If the dough feels dry or crumbly, add more cold water, 1 tsp at a time, until it just comes together. If the dough is too sticky, add a bit more flour. Knead gently in the bowl to make sure all ingredients are incorporated.
Wrap in plastic wrap and allow to chill in the refrigerator for 15-30 minutes (this helps it roll out more easily). If you're short on time, you can skip this step and try to roll the dough out without chilling.
After the dough has chilled, preheat the oven to 350°F (175°C).
Place the dough between two sheets of parchment paper, and roll it out as thin as possible, about 1/8 inch thick. Peel off the top piece of parchment paper, and transfer the bottom sheet with the dough onto a baking sheet. Use a knife or pizza cutter to score the dough into squares or desired cracker shapes. Prick each cracker lightly with a fork to prevent puffing during baking.
If desired, brush the tops of the crackers with melted butter. Sprinkle flaky sea salt evenly over the crackers.
Bake the crackers for 20 to 25 minutes or until golden and crisp. Remove from the oven and allow to cool completely on the baking sheet before breaking apart along the scored lines.
Store in an airtight container for up to one week.
Notes
For best results, roll the dough to about 1/16 to 1/8 inch thick. Thinner dough yields crispier crackers.Personally I prefer to use dried sage inside the crackers. I find that the flavor get distributed more evenly. But you can also use fresh sage. Use 1 tablespoon of fresh sage in place of 1 teaspoon dried.Use a block or parmesan cheese and grate it for better flavor.These crackers pair beautifully with creamy cheeses like Brie or goat cheese, tapenade, or fall dips like roasted butternut squash or pumpkin hummus.