Begin by melting your butter and allowing it to cool while you gather the rest of your ingredients.
In a stand mixer, combine the potato flake sourdough discard starter, flour, salt, flax seeds, and cooled butter. Be sure the butter isn't too hot, as it can harm your starter.
Attach the dough hook and knead the mixture on low speed for 5-10 minutes until a ball forms. Start on low speed, then switch to medium for a minute or two to help the ball come together before returning to low speed. If the dough is not coming together, and the dough is too sticky, add a bit more flour. Be careful to not add too much flour, just a tablespoon at a time.
Once the dough is kneaded, cover the bowl with plastic wrap or another airtight cover and let it ferment at room temperature for 8-12 hours. You can extend this time for up to 24 hours for more flavor development.
After fermentation, preheat your oven to 350 degrees Fahrenheit. If you have a baking stone or pizza stone, place it in the oven to preheat.
Divide the dough into 4 equal pieces using a bench scraper. Keep three pieces covered to prevent them drying out while working with the first section.
Press the dough flat onto a piece of parchment paper.
Place another piece of parchment paper on top and roll the dough as flat as possible.
I find it easiest to use a rolling pin that has adjustable thickness rings. If you have one like this, use the thinnest setting, getting the dough as thin as it will allow. Once it is rolled out, remove the thickness rings and roll out even thinner.
See the post on additional info on how to get it evenly thin.
Remove the top parchment paper and sprinkle the top of the dough with coarse or flaky sea salt and any desired seasonings. Gently press the seasoning into the dough, either with your bare hands, or by placing the parchment paper back on top and gently pressing.
If using the top parchment, carefully remove it. Use a fork to dock holes all over the sheet of cracker dough to prevent puffing during baking.
Use a pizza cutter to cut the dough into approximately 1-inch squares.
Slide the parchment paper with the dough onto the preheated stone or baking sheet.
Bake the crackers at 350°F for 8-10 minutes. This time can vary based on how thick the crackers are and how crispy you want them. Watch closely towards the end to prevent burning.
Remove any crackers that brown faster than others and continue baking the rest.
Repeat this process with the remaining dough pieces. Remove the crackers from the baking sheet and allow the crackers to cool on a chopping block or plate before storing.
This recipe yields about 6-7 cups of crackers. Store them in an airtight container at room temperature for up to a week for best results.