Preheat oven to 375F. and grease two baking sheets.

In a food processor blend together butter and cheese until smooth. Add egg yolk, salt, and cayenne and blend until combined. Add flour and blend until mixture just forms a dough.

Working in batches, transfer dough to a pastry bag fitted with a 7/8-inch-wide ribbon tip and pipe dough in long strips 2 inches apart on baking sheets. (Alternatively, working in batches, dough may be transferred to a cookie press fitted with a ribbon disk and pressed out in long strips 2 inches apart on baking sheets.) Dough strips may break in places but repairs are not necessary, as strips will be cut later.

In a small bowl whisk together egg white and a pinch salt until just combined. Brush each strip of dough with some egg white and bake in batches in middle of oven until golden brown, about 10 to 15 minutes. While crackers are still hot, slice diagonally into 1 1/2-inch-long pieces and cool completely on racks. Crackers keep in airtight containers 5 days.

Makes about 95 crackers.