Fill a large pot with water and put it on the stove to boil then preheat oven to 400F.
Once the water is boiling, add the diced potatoes and cook until very tender, about 10 minutes.
Drain potatoes and transfer to a large bowl then mash with cream, butter, salt and pepper.
Slice the white part of the leek into quarters lengthwise, then slice into half inch pieces. Place the leeks in a bowl and cover with cold water to soak. Let stand at least 10 minutes to let sand and soil fall to the bottom. Scoop leeks from the top of the water and rinse again.
Return the pot to the stove and melt butter over medium high heat.
Add the leeks and carrots to the pot, sauteing until the vegetables soften a little, about 4-5 minutes.
Deglaze the pan with the wine, cooking until the alcohol smell burns off.
Sprinkle the flour onto the vegetables while stirring constantly and then cook for one minute.
Pour in the stock and cook the mixture until its bubbly and thick, stirring often.
Stir in the chicken and thyme and season with salt and pepper to taste.
Transfer the filling to the bottom of a tall casserole dish roughly 8 by 12 inches in size.
Spread potatoes on top of filling then sprinkle with grated cheese.
Bake 25 minutes, or until the filling is bubbly and the top is browned.
Let the cottage pie rest for 10-15 minutes then garnish with parsley and serve.
Our casserole dish which is 8x12 inches holds 3 quarts of liquid. You can use an oval dish or a standard 9x13 pan.
We suggest using dark meat because it can stand up better to the double cooking time but you can use whatever leftover chicken you have on hand.
This is a great dish to prep for weeknights or dinner parties. Layer the casserole then cover with foil and refrigerate until ready to bake. Keep in mind that it will take longer to bake when it's cold.
Choose a full bodied white wine as it will enhance the flavor of the dish.