In a large bowl, mix together all of the dough ingredients until it forms a cohesive ball. The dough should be soft but not sticky. If the dough is too dry, add water 1 teaspoon at a time until it comes together. If the dough is too wet, add flour 1 teaspoon at a time.
Divide the dough in half and cover tightly with plastic wrap. Place in the fridge for at least 45 minutes to allow the dough to firm up. The dough can be left in the fridge for up to two days before baking.
Preheat the oven 350°F.
Place half of the dough in between two sheets of parchment paper. Then use a rolling pin to roll it to about ⅛th of an inch thick. Carefully peel off the top sheet of parchment paper. Transfer the parchment paper to a baking sheet. Repeat with the other half of the dough.
Using a sharp knife or pizza cutter, cut the cracker dough into 1 inch squares. Gently prick each square with a fork to help air escape in the oven.
Lightly brush the tops of the crackers with melted butter and sprinkle with flaky sea salt.
Bake the crackers at 350°F for 20-30 minutes (rotating the pan halfway through baking) or until golden brown and crisp on the edges. Turn off the oven and crack the door open slightly. Leave the crackers in the turned off oven to allow them to cool and continue drying out.
Once the crackers are completely cool, store in an airtight container at room temperature for up to two weeks.