1 lb. pkg. frozen puff pastry
1 tbsp. Dijon mustard
1/2 lb. thin sliced ham
1/2 lb. thin sliced cheese
1 egg

Thaw pastry. Combine mustard and 1 teaspoon water. Roll 1 sheet of pastry on a floured work surface to a 10 x 15 inch rectangle. Transfer dough to an ungreased baking sheet. Spread with mustard to within 1/2 inch of the edge. Cover with half the ham and then half the cheese. Top with a second layer of each. Refrigerate. Roll a second sheet of dough to a 10 x 15 inch rectangle. Using a sharp knife, score a cross-hatch pattern in the dough.

Remove baking sheet from refrigerator. Brush edges of dough with water. Cover with scored rectangle and press edges to seal. Cover with plastic wrap and refrigerate at least 30 minutes. Heat oven to 400 degrees. Beat egg with 1 tablespoon of water. Brush about 1/3 of this mixture over the top of the pastry. Bake until puffed and golden, about 25 minutes. Cool about 10 minutes. Trim edges and cut into squares.