Preheat the oven to 325 degrees.
In a medium bowl, mix together all the ingredients except the flaky salt. Let sit for 15 minutes to firm up.
Lay a large sheet of parchment paper on the counter and use a spatula to scrape the seed mixture onto the paper. Top with another piece of parchment and use a rolling pin to roll the mixture into an 8 x 11-inch, 1/4-inch thick sheet. (I used a ruler to measure this.)
Transfer to a baking sheet and carefully peel off the top layer of parchment (go slowly, as a few seeds may stick to it.) Sprinkle with flaky salt and bake for 45 minutes. If the crackers don't seem dried out on the bottom, turn off the heat but leave the pan in the oven with the door closed for 30 minutes. Check the crackers and leave them in longer if necessary.
Allow to cool, then break the cracker into large pieces and store in an airtight container for up to 1 week.