Quarter the onions and the celery stalks.
Zest and juice the lemon, separating the zest and juice into separate bowls.
In a large saucepan, bring the raw chicken or chicken pieces, stock, onion, celery, and the zest of the lemon zest to a boil.
Cover, lower the heat, and simmer for 30 minutes.
Quarter the carrots and potatoes and add to the pot.
Cover and simmer for another 20 minutes.
With a slotted spoon, remove the veggies and place them on a cutting board.
Slice the veggies into bite-sized pieces and place in a clean bowl.
With tongs, remove the chicken and place it on the cutting board.
Skin and debone the chicken. Compost the bones. And, either reserve the skin for another use, compost it, or feed it to the dog!
Cut or shred the chicken into bite-sized pieces and add it to the bowl of vegetables.
Skim the fat from the cooking liquid and bring it to a boil.
Into a heat-proof glass measuring bowl, pour about 800ml [about 3 1/2 cups] of the cooking liquid. [The rest may be reserved in a separate container as stock for future use. If, for some strange reason, you don't have enough liquid to measure, top it up with additional stock, white wine, or water.]
Melt the butter in the microwave or in a small pot.
Add the flour and whisk with a fork for about 60 seconds.
Add the butter flour mixture to the large, empty cooking pot.
Turn the heat on medium-high.
Skim the fat from the stock and slowly add it back to the pot, whisking with a flat whisk or wooden spoon until it boils and thickens up a bit.
Turn the heat off.
Add the lemon juice and whiskey.
Add salt and pepper to taste.
Remove from heat.
Add the frozen peas and stir to incorporate.
Stir the chicken and vegetables into the sauce.
Allow the mixture to cool for at least 1 hour before continuing with the crust and the final bake!