Mix the butter and powder sugar in a large bowl until it looks like cream. Add yoghurt and egg and mix them all together. Slowly add flour, baking soda and vanilia in the cookie mix. Knead them until it looks thick. Rest the dough until it's fully ready and looks soft. To prepare the inside of the cookie; grind the apples with the bigger side of the grater. Cook them until it takes in the water with castor sugar. Add the chestnut and cinnamon, mix them all together and take it off the oven. Wait until the apple mix cools down to keep your cookies in shape. Take small pieces out of the dough. Pour some flour on the kitchen counter and roll them to give them a circular shape. Do the same for all the dough pieces. Put the apple mix in the middle of the circular dough and roll them to give them shape with your palm. Place them on the oven tray with baking paper seperately. Heat them for 20 minutes in the previously heated oven with 170 degrees. Ready to serve! Enjoy!
You can add or remove half glass of flour depends on the density of the dough. To give a good shape to the cookies, cover the dough with sling wrap and put it in the fridge for 15 minutes.