3/4 teaspoon cornstarch

1/4 teaspoon ground mustard powder

1/2 cup evaporated milk

1/8 teaspoon Worcestershire sauce

1/8 teaspoons hot sauce, such as Tabasco

Kosher salt and black pepper, to taste

3 ounces diced prosciutto or ham

1 large egg, lightly beaten

Unwrap one sheet of puff pastry on a clean work surface. Using a pizza cutter or sharp knife, cut the pastry lengthwise into 3 wide strips of equal size (follow the seams as a guide). Cut each strip in half crosswise for a total of 6 equal-sized rectangles. Transfer the rectangles to a parchment-lined baking sheet and repeat with remaining pastry sheet. Transfer the baking sheet to the refrigerator while continuing with the recipe.

Combine cheese, cornstarch and ground mustard powder in a small saucepan and toss to combine. Add evaporated milk, Worcestershire and hot sauce and cook over low heat, whisking occasionally, until melted and smooth, about 5 minutes. Season with salt and pepper, to taste. Stir in the prosciutto and set aside to cool slightly and thicken up.

Sort through the rectangles and remove the 6 widest to use as the tops, keeping the 6 thinner rectangles on the baking sheet to fill. Mound 2 to 3 tablespoons of the cheese mixture onto each rectangle, leaving a 1/2-inch space along the edges. Brush the space along the edges with the beaten egg and top with the larger rectangles of pastry. Gently press the edges of each pocket to adhere. Press a fork along all the sides to fully seal. Transfer the baking sheet to the freezer for 15 to 20 minutes before baking.

Meanwhile, preheat oven to 400 F. Remove the pan from the freezer. Lay a sheet of parchment over the "pockets" and nestle another baking sheet on top -- this will prevent the pastry from puffing too high. Transfer the sheet pan(s) to the oven and bake for 15 minutes. Transfer the oven rack to the broiler position and remove the top baking sheet. Adjust oven setting to broil and continue cooking the pockets, rotating the pan as needed, until golden brown, 2 to 3 minutes. Cool for 10 minutes before serving.

To freeze the pockets, bake according to directions and allow them to cool completely. Freeze in a single layer on a baking sheet, then transfer to an airtight zip-top bag and return to the freezer. To reheat, cover in aluminum foil and warm in a 350 F oven, or cook in the microwave for 2 to 3 minutes until hot.

(Nealey Dozier is a writer for TheKitchn.com, a nationally known blog for people who love food and home cooking. Submit any comments or questions to kitchn@apartmenttherapy.com.)