Cut chicken into pieces. Heat oil in a large pot, stirfry 1/2 whole onion, 1/3 whole carrot, celery stem and garlic cloves together with chicken backbone, breast and thighs and interiors if available (reserve drumsticks and wings for a different dish); flip once or twice until browned. Add salt, pepper, oregano, leek leaves and boiling water (2 lt.). Boil for 1/2 hour medium high heat, covered, then let simmer for additional 15m-30m. Reserve chicken and strain stock, discard veggies.
While chicken is cooking, make dough according to recipe. Divide dough in 2 and reserve each ball in plastic film, room temperature.
When you are done with the dough, add oil to a pan and stirfry chopped onion, carrot, leek and celery. Reseve. Stirfry bacon (optional) and mushrooms. Reserve together with the rest of the veggies.
When the chicken has cooled down, remove meat from bones and cut in bite size pieces (size to taste). Be sure to prevent bone or cartilage to mix with the meat. Discard bones.
Heat butter in a pan, add flour and stir until browned. Slowly add broth to create a gravy-like consistency. Add reserved stirfried veggies, add chicken meat, add green peas, add olives. Here's where you can be creative and add/remove/replace any of the ingredients (but if you remove the chicken, it's not a chicken pie anymore ).
Add stock and make it slightly more liquid that the consistency you want inside the chicken pie. Season to taste and let simmer for 5 to 10 minutes or until you reach the consistency you desire. Turn oven on and preheat @ 200C.
Roll half of the dough and lay it in the pan, covering the edges and leaving excess to fold the dough (use ~1 to 2 inches high pie pan). Roll top dough to make sure it covers the pan. (There should be some excess dough that you can use for decoration or some extra biscuits). Fill the bottom dough with the mix in the pan, making sure it does not overflow.
Cover with top dough, cut excess dough off and stick edges together and roll them in. Use part (or all) of the excess dough to add ornaments to the dough.
Brush eggwhite on top of dough and make small wholes evenly to let steam escape.
Bake in oven for 20-30 mins, until top crust is cooked and browned. Let rest for 5-10 mins before serving.
