PREPARATION:

1. Preheat oven to 400°F. Grease baking sheets.
2. Roll out 1 sheet puff pastry dough on well floured surface to 14x10-inch rectangle. Spread half of dough (from 10-inch side) with mustard. Sprinkle with cheese and pepper. Fold dough over filling; roll gently to seal edges.
3. Cut lengthwise into 3 strips; cut each strip diagonally into 1-1/2-inch pieces. Place on prepared baking sheets. Beat egg and water in small bowl; brush onto appetizers.
4. Bake appetizers 12 to 15 minutes or until puffed and deep golden brown. Remove from baking sheets to wire rack; cool.