Preheat oven to 450 degrees. Grate cheese. Sift flour, salt, cayenne & mustard into large bowl. Cut in butter and mix until fully combined (this can be done in a food processor). Stir in cheese and then knead with hands until batter comes together. If necessary, add small amount of ice water.
Roll into ball, wrap in plastic and refrigerate for 20 minutes (this can be done up to 2 days in advance of cooking). When dough is chilled, roll to about 1/4" inch thick and cut into strips about 1/2" wide. Place on slightly greased baking sheet and bake until golden, about 8-10 minutes.