How to Make It
Process cheese, flour, cornmeal, cornstarch, salt, dry mustard, and pepper in a food processor until combined, about 5 seconds. Add butter, and process until mixture resembles wet sand, about 20 seconds. With processor running, add water through food chute; process until dough forms a ball, 10 to 15 seconds.
Divide dough in half, and shape each half into a 6-inch log, about 1 3/4 inches in diameter. Wrap logs individually in plastic wrap; chill at least 1 hour or up to 2 days.
Preheat oven to 350°F with oven racks in upper and lower thirds. Unwrap logs, and slice into 1/8-inch-thick rounds. Place dough rounds, 1/2 inch apart, on 2 parchment paper-lined baking sheets.
Bake in preheated oven until edges are golden brown, about 14 minutes, rotating baking sheets top to bottom halfway through bake time. Cool crackers on baking sheets 5 minutes. Transfer to a wire rack to cool completely, about 20 minutes.