In deep skillet, bring chicken, stock, parsley, celery and bay leaf to simmer. Cover and cook for 20 minutes on medium-low heat.
Add carrots and onions, cook for about 10 minutes (cooked but still firm).
Remove chicken and let cool.
Transfer carrots and onions to 1.5 ltr casserole dish. Discard parsley, celery and bay leafs.
Cut chicken into 1-1/2 inch chunks and add to casserole along with the ham and peas.
In small dish blend flour with butter until smooth. Stir in a few tbs of stock to make paste. Blend back into remaining stock in skillet, bring to simmer and cook until thickened (3 - 4 minutes) stirring constantly.
Pour into casserole and cool.
Fit pastry over casserole and seal edges. Cut slits for steam.
Bake at 425°F for 10 minutes.
Reduce heat to 350°F and cook for another 50 - 60 minutes, until filling is bubbly.
If pastry begins to get too brown, cover with foil while cooking.
****For freezing for later use either freeze filling and make the crust and bake when ready to eat OR make pie but freeze before baking and bake it when ready to eat it.