This is an adaptable little recipe. We love the warm, spicy flavor of brown mustard, but feel free to use your favorite kind. You can also customize the filling by using any kind of thinly sliced cheese and/or meat that you prefer.
Preheat oven to 400° and line a baking sheet with parchment paper.
Roll puff pastry into a 12-in. square. Cut into 8 rectangles, 3 by 6 in. each.
Spread 1/4 tsp. mustard on half of each rectangle, leaving a 1/4-in. border at edges. For each, top mustard with 1/8 of cheese, then 1/8 of loosely bunched ham ribbons. Brush border with water. Fold empty dough half over ham and cheese and crimp edges with a fork to seal.
Put hand pies on prepared baking sheet. Cut a few slits in top of each pie. Bake until brown and crusty, 20 to 25 minutes. Cool on a rack, then chill in an airtight container. Bring to room temperature to serve.
Make ahead: Up to 2 days, chilled airtight.
* Percent Daily Values are based on a 2,000 calorie diet. Your daily value may be higher or lower depending on your calorie needs.