Shred cheese. If possible shred cheese using the shred blade in your food processor. Remove shredding blade and cheese from food processor and replace the blade with the normal blade.
Add cheese, flour, butter, ground mustard, and salt and pulse until the mixture crumbles.
While pulsing, add one Tbs of water at a time until dough comes together.
Remove from food processor, form ball, wrap in plastic wrap and put in the refrigerator for 20 minutes.
Preheat oven to 350.
Roll dough thin, cut into one inch squares. Using a pastry wheel or a pizza cutter works as well. Us the tip of a skewer to poke a hole in the center of each square.
Sprinkle with coarse kosher salt
Bake for 15 minutes. But watch them carefully. The high fat content makes them to from crispy to over baked fast!
Let them cool and enjoy!