Mix together the dry ingredients in a large mixing bowl. Add in the butter, using your hands or a pastry blender to break the butter into coarse crumbs with the dry ingredients, like you would if you were making pie crust or shortbread.
Combine the vinegar with three tablespoons of water, and add to the flour mixture. Mix with a wooden spoon, adding more water by tablespoonfuls if necessary. Just keep stirring until the dough starts to come together. Once you have a nice, smooth ball of dough formed, wrap it in plastic wrap and refrigerate for at least an hour.
After the dough has chilled, remove it from the refrigerator and divide into two equal halves. Roll the dough out as thin as possible onto a floured sheet of parchment paper (the parchment paper will really help). Cut the dough into 1-inch squares (a rolling pizza cutter comes in handy for this), and prick a hole in each square with a fork (this allows steam to escape so the crackers don’t puff up). Transfer the parchment paper to a baking sheet and bake in a 375F oven for about 10 to 14 minutes. They burn quickly, so keep an eye on them. I checked them, and rotated the pans, at the seven minute mark. The first batch took 14 minutes, but the second took barely 10.