Season chicken (bone in/ skin on) breast with salt and pepper and roast in oven until internal temp reaches 170 F. Once cooled remove skin and shred. **You may also use store bought rotisserie chicken for faster prep.**
Saute all filling ingredients except milk. Cook for 5 minutes, add milk and cook for another 3 minutes. Let cool while making dough.
Mix sugar, salt, and flour. Cut in butter using a blender or 2 knives until it resembles coarse cornmeal. Sprinkle water and mix well with hand to form ball. Knead lightly. Sprinkle flour on a board and roll out dought into 1/4" thick. Cut using a round cutter. Fill each cut dough with 2 tbsp. of sauteed filling. Fold dough to form a half moon and press one end to the other. Brush with egg yolk or milk. Arrange on a greased (or parchment lined) baking sheet and bake at 350 degrees preheated oven until crust is golden brown.