Instructions:

• Step 1: Preheat your oven to 400°F (200°C) for even baking.
• Step 2: In a mixing bowl, combine the crumbled feta, grated kashkaval, ricotta cheese, and the large egg. Season with salt and pepper to taste. Mix until well combined and set aside.
• Step 3: Roll out each sheet of puff pastry on a lightly floured surface until about 1/8 inch thick.
• Step 4: Cut the rolled pastry into squares or rectangles, about 4 inches on each side.
• Step 5: Place about 1 tablespoon of the cheese filling in the center of each pastry square, being careful not to overfill.
• Step 6: Fold the pastry over the filling to form a triangle or rectangle. Press the edges together to seal and crimp with a fork.
• Step 7: Beat the egg yolk and brush it over the top of each boureka.
• Step 8: Sprinkle sesame or poppy seeds on top if desired.
• Step 9: Place bourekas on the lined baking sheet, spray lightly with cooking oil, and bake for 20-25 minutes until golden brown.
• Step 10: Allow to cool slightly before serving warm or at room temperature.