You'll have to discard any scraps, since this dough can't be rolled out again.
Preheat oven to 325 degrees. Pulse flour, table salt, and sugar in a food processor to combine. Add butter, and pulse until mixture resembles coarse meal. With machine running, gradually add milk; process until dough comes together.
Transfer dough to lightly floured surface. Roll into 10-by-12-inch sheet, 1/16 inch thick . Sprinkle with kosher salt; gently roll to press salt into dough.
Cut dough into 2 1/2-inch squares; carefully transfer to a baking sheet. Liberally pierce with a fork. Bake until just brown and firm to touch, 20 to 25 minutes. Transfer to a wire rack to cool. Store in an airtight container.