Whirl the first four ingredients in the bowl of a food processor. Add the butter and process until the mixture looks like coarse meal. Working quickly, turn on the food processor and pour the ice water through the feed tube, stopping before the dough comes together. Pinch a bit of the dough between your fingers. If it does not stick together, add a teaspoon more water and whirl briefly.
Turn the dough out onto a large piece of plastic wrap. Use the plastic wrap to help you create a flat disk: fold the edges of the dough toward the center and press down to smooth out the roughness. Refrigerate dough for about 15 minutes.
Roll the dough about 1/8-inch thick on a well-floured piece of parchment paper. Using a pizza cutter and a ruler, trim the dough into 1/2-inch squares, rectangles, or diamonds. Carefully transfer the cracker-lined parchment paper to a baking sheet. Don't worry about separating the crackers before baking.
On the middle rack of an oven preheated to 375° F, bake the crackers until they just start to turn pale brown, about 15 minutes. Turn the oven off and crack the door open, leaving the crackers inside to cool and continue to crisp, about 30 minutes more. Remove from the oven and allow to cool completely. Separate crackers gently and serve. Store in a sealed container for up to a week.