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Preheat the oven to 400°F. Get out several large baking sheets; no need to grease them.
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Whisk together the flour, salt, pepper, and Parmesan.
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Add the cold butter, working it in until no large pieces remain; a mixer works well here.
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With the mixer running (or stirring all the while), drizzle in milk until the dough comes together; you may not use the entire 1/2 cup.
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Gather the dough into a ball, and squeeze it a few times to bring it together. Divide it into three pieces. If you have a scale, they'll weigh about 6 1/2 ounces (187g) each.
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Working with one piece of dough at a time, flatten it into a rough square, and place it on a lightly floured work surface. Roll the dough 1/8" thick; it'll be about 10" square (or an 11" circle, if your rolling efforts result in a circle).
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Transfer the dough to a piece of parchment or aluminum foil. Using a sharp knife, pizza cutter, or pastry wheel, cut the dough into 1" squares; don't separate them. You may trim the edges first, if you like, in order to separate the "good looking" crackers from the raggedy ones around the edges.
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Lift the piece of parchment/crackers onto a baking sheet. Sprinkle the crackers with coarse sea salt, additional grated cheese, and/or dried herbs.
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Repeat with the remaining pieces of dough.
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Bake the crackers for about 15 minutes, until they're a medium golden brown. Remove them from the oven, and cool right on the pan.
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When the crackers are cool, store them airtight at room temperature.
