Preparing chicken filling:In a large pot, cover the potato cubes with water, add a pinch of salt, and cook for 10 minutes over high heat. The potatoes should be tender when tested with a fork. Drain and set aside.
In a large pan over medium heat, add the olive oil, the onion, and cook for 3 minutes until soft.
Add the ground chicken, crush it with a spatula and cook for 5 minutes.
Add the drained potatoes and peas to the chicken mixture. Mix all together with a spatula for 1 minute until well combined.
Add the ginger, turmeric, cumin, coriander, mustard, garam masala, salt and pepper. Cook for 10 minutes until the chicken mixture and the spices are well incorporated. Remove the pan from the heat.
In a medium bowl, press 3 Kiri square portions with a spatula until the texture becomes smooth and creamy.
Add the pressed Kiri to the chicken mixture and mix well with a spatula until well combined.
Cut the remaining Kiri square portions into small cubes and add it to the chicken filling. Allow to cool.
Assembling the samosas:On a floured working surface, spread the samosa dough until it is 1 mm thick. Cut the samosa dough into squares of 10cm.
Place a full teaspoon of the filling close to one edge of the squares. Fold into a triangle shape then press the edges so they stick. Using a cutter, remove the excess of the samosas.
In a small bowl, mix the egg yolk and white vinegar, and brush the chicken samosas surface.
Place the samosas in an oven pan covered with parchment paper and brush them with the egg yolk mixture.
Bake the samosas in a preheated oven at 180C (365F) for 30 minutes until golden brown.
Serve the chicken samosas with yogurt and parsley sauce.