1(17.3-to-18.3 ounce) package puff pastry(contains 2 sheets, folded into thirds or rolled–depending on brand)
1 ¾ to 2cupsgrated or crumbled feta cheese(we recommend Bulgarian feta)
1tablespoonfinely chopped parsleyoptional
Preheat the oven to 400°F. Line 2 baking sheets with parchment paper.
If using Pepperidge Farm brand puff pastry which is folded into thirds:
Thaw the puff pastry and unfold it. Flour generously so it doesn't stick to your work surface. Cut it along the folds into three strips. Gently roll each piece lengthwise on a lightly floured surface until it is about 10 to 11 inches in length. Then cut each long rectangle into three squares. Each puff pastry sheet will yield 9 squares, 18 in total between both sheets. These boreks will be a bit larger.
If using another puff pastry brand which is rolled:
Thaw the puff pastry and unroll it. Flour generously so it doesn't stick to your work surface. Cut into four strips width-wise and then three strips lengthwise. Each puff pastry sheet will yield 12 squares, 24 in total between both sheets. These boreks will be a bit smaller. You can make them even smaller but cutting these sheets into 16 squares each to yield 32 mini boreks.
If using parsley, mix it into the feta cheese. Place a heaping tablespoon of feta cheese into the center of each square, packing it together (use a bit less for the smaller boreks). Fold the squares into either triangles or rectangles depending on your preference. Press the edges together with your fingers and then the tines of a fork to seal them well (they should seal easily, but if they do not, feel free to brush egg wash along the edge before pressing the dough together).
Place the boreks on the parchment-lined baking sheets and brush the tops with the beaten egg. Bake for about 18 to 20 minutes, switching the pans from top to bottom halfway through, until the tops are golden brown. Allow the boreks to cool slightly and serve either warm or at room temperature. The boreks are freshest served the day they are baked, but if necessary store leftovers in a sealed container at room temperature.
If using a more firm Greek feta, grate the cheese on a box grater instead of crumbling it (Bulgarian feta is usually too soft to grate, it may simply fall apart).
To make meat borek, replace the cheese with an equal amount of gheyma. If making both types at once, fold one into triangles and the other into rectangles to differentiate.