Make the eggplant filling: Heat the oil in a pot over medium high heat. Once the oil is hot, add the eggplants and onions. Fry until golden brown, about 30 to 40 minutes, stirring occasionally. Add the tomatoes and cook for another 20 minutes. Place the mixture in a strainer set over a large bowl. Set aside for 1 hour to drain the mixture from excess oil. Discard the excess oil, add the blue cheese and salt into the mixture. Mix until combined well. Set aside.

Make the cheese filling: Place the potato into a small pot. Cover the potato with cold water and set over high heat. Bring the water to a boil, lower the heat to a gentle simmer and cook until the potatoes are fork tender, about 40 minutes. Transfer the potato out of the pot with a slotted spoon and set it aside to cool for about 10 minutes. Peel the potato and place it into a mixing bowl. Using a fork, smash the potato well until it is the consistency of mashed potatoes. Add the ricotta, kashkaval, egg and salt. Mix well until combined. Set aside. 

Make the dough: Place the water, oil and salt into a food processor. Blend until the mixture becomes white, about 1 minutes. Add the baking powder and flour and blend until the mixture forms a dough, about 3 to 5 minutes.

Preheat the oven to 350 degrees.

Turn the dough onto the counter. Roll it into a ball, cut it into 4 pieces of dough. Roll out each piece to a 12 inch long log. Starting with one log of dough, cut it into 7 pieces crosswise. Roll one piece of dough into a disk-like shape, about 2 inches in diameter, using the palms of your hands. Place the rolled dough onto the counter. Continue shaping the remaining 6 pieces of dough. Repeat with the remaining 3 logs of dough. Cover all the rolled out pieces of dough with a towel and set aside for 20 minutes. 

Shape and fill the borekitas: Take one piece of rolled out dough. Flatten out the piece of dough with your fingers until it is about ⅛ inch thick. Starting with the eggplant filling, place about ½ tablespoon of the mixture into the center of the dough. Take one edge of the dough and fold it over to seal the filling, forming a semicircle shape. Pinch the seams of the dough together. Using your index finger and thumbs, twist and pinch the seam of the dough to create a crimp like pattern across the round edge. Place the borekita upright onto the parchment paper, with the seam side up. Continue with the remaining 13 pieces of dough. Use the potato and cheese filling for the remaining 14 pieces of dough. For the potato and cheese filled borekitas place them on the parchment paper sideways so the seam side is on the side of the pastry. Brush all the borekitas with egg wash. Sprinkle the eggplant filled borekitas with sesame seeds. Sprinkle the potato and cheese filled borekitas with grated kashkaval.

Transfer the borekitas to the oven and bake for about 40 to 50 minutes until golden brown.

Serve hot with a side of boiled eggs and plain yogurt.