In a large bowl, mix the flour with the salt, pepper, and mustard powder.
Using a pastry cutter or two knives, cut in the butter until the mixture resembles breadcrumbs. Mix in the grated cheese.
Sprinkle the water over the flour mixture, a little bit at a time, mixing gently. The dough should just be able to come together.
Turn the dough onto the counter and knead lightly.
Roll out the dough until it's just less than 1/4" thick.
Cut out 3" rounds, rerolling scraps and recutting as necessary. Set aside. You should have about 18 rounds.