In the food processor or in a large bowl, combine 1 1/2 cup flour, salt, cayenne and ground mustard. Cut the butter into the flour mixture until it resembles coarse meal. Then stir in the cheese.

In a separate bowl, mix together the egg yolks and the water.

Add the egg mixture to the flour mixture and blend to form a dough that will hold together in a cohesive ball.

Add more flour as needed, to make a workable dough. Then wrap the dough in plastic wrap and chill one hour.

Divide the dough into two equal portions, roll out on a floured surface to a circle approximately 1/2 inch thick (the dough will be crumbly and a bit hard to manipulate, but don't let this worry you, it doesn't hurt the final product).

Cut this circle in four equal "pie" segments. Gently lift each of the segments one at a time and, without rotating them, stack them on top of each other so that the straight edges form the sides of a square.

Press this gently and roll it out again (this is what makes the cracker flaky). Repeat cutting, lifting and rolling out two more times. Roll the dough thinner the last time, about 1/8 inch thick.

If desired, sprinkle top lightly and evenly with salt and roll over it lightly with the rolling pin. With a sharp knife (or rolling pizza cutter, if you have one), cut the dough into 1-inch squares and place them on an ungreased baking sheet.

Prick each square 1 or 2 times with the tines of a fork, and bake at 350°F for 10 minutes.

Remove any crackers that are already browned through. Turn the rest and bake an additional 5 or 6 minutes, or until medium brown.