In a large sauté pan, heat 1 tablespoon oil over medium-high heat and sauté onions for 3 to 4 minutes. Add apples and cook for 2 minutes, or until tender. Stir in maple syrup and vinegar. Let sizzle until all liquid is reduced.

Remove apple mixture and add remaining oil to the pan. Over medium-high heat, stir-fry chard until it is dark jade green and no liquid remains. Stir into apple mixture. Add hazelnuts and cranberries and season with salt and pepper. Let cool completely then gently fold in cheese.

In a small bowl, beat egg well with water; set aside (this is called an “egg wash”).

Unfold each sheet of puff pastry and cut each into 9 (3-inch) squares. Very lightly brush the surface of each square with egg wash (just enough to make it sticky, not wet).

Place a scant tablespoon of filling in the center of each square and fold the edges to form a triangle. Press down to seal the edges well, and use a knife to trim any uneven edges.

With the tip of your knife, cut a small slit in the top of each pastry to vent during cooking. Brush the top of each turnover with a light coating of egg wash and place on a parchment-lined baking sheet. You may bake them right away, or place the baking sheet in the freezer, freeze individually, then place them in a freezer bag for later use.

To bake, preheat oven to 425° F. For fresh pastries, bake for 15 to 20 minutes, or until deep golden brown. To cook frozen pastries, do not thaw; bake for 20 to 25 minutes,until deep golden brown.