Preheat the oven (with one of its racks positioned in the center) to 500°F for at least 45 minutes before you plan to bake the matzo. Line 2 large baking sheets with parchment paper and set them aside.
Meanwhile, in a large bowl, mix together the flour and kosher salt. Make a well in the center and add ¾ cup cold water and the olive oil. Using a wooden spoon, mix until the dough comes together, adding up to an additional ¼ cup of water, one teaspoon at a time, if needed. Lightly flour a clean work surface, turn the dough out onto it and knead until it comes together in a mostly-smooth ball, about 5 minutes. Divide the dough in half, then cut each half into 6 equal pieces (about 1½ ounces each). Place the 12 pieces on a piece of parchment paper, cover with plastic wrap, and set aside to rest at room temperature for 20 minutes.
Lightly flour your work surface again, then use a rolling pin to sheet one of the pieces of dough out to a 6- by 4-inch rectangle. Transfer the sheet of dough to one of the parchment-lined baking sheets, then prick it all over with a fork. Repeat with the remaining pieces, fitting 4 matzos on each sheet. Transfer one pan of crackers to the oven and bake until just the matzo is beginning to brown in spots on the bottom, 4–6 minutes. Using tongs, flip the crackers and continue baking until just crisp, 2–4 minutes more. Remove from the oven, brush lightly with olive oil, and sprinkle with flaky sea salt if desired. Continue baking the rest of the dough, one pan at a time, in this manner until all of the matzo is cooked. Serve warm or at room temperature. Cooled matzo crackers will keep in an airtight container for up to one week.