-
1
Make filling: Bring the broth to a boil in a saucepan.
-
2
Add the carrot and celery and cook until tender, about 4 minutes.
-
3
Using a slotted spoon, transfer them to a plate.
-
4
Pour enough of the broth into a liquid measure to make 2 1/2 cups.
-
5
Set aside.
-
6
Heat the butter in a large saucepan over medium-high heat.
-
7
Add the mushrooms and cook, stirring, until lightly browned, about 6 minutes.
-
8
Add the shallot, bay leaf, thyme, and tarragon and cook, stirring, until soft.
-
9
Stir in the flour and cook, stirring, for 3 minutes.
-
10
Gradually stir the reserved broth, wine, nutmeg, and season with salt and pepper.
-
11
Bring the sauce to a boil, lower the heat, and simmer, stirring occasionally, about 4 minutes.
-
12
Add the carrot, celery, chicken, onions, and peas and return to a boil.
-
13
Stir in sherry and remove the chicken mixture from the heat.
-
14
(Filling may be made 1 day ahead, cooled, uncovered, and chilled, covered.)
-
15
Preheat oven to 425 degrees F.
-
16
Make mashed potatoes: In a saucepan cover potatoes with water by 1 inch and simmer until very tender, 10 to 15 minutes.
-
17
Reserve about 1/3 cup cooking liquid and drain potatoes.
-
18
In batches, force potatoes through a ricer into a bowl.
-
19
Stir in sour cream, chives, and enough reserved cooking liquid to reach a fluffy consistency.
-
20
Season with salt and pepper, to taste.
-
21
Transfer potatoes to a pastry bag fitted with a 1/2-inch fluted tip.
-
22
Spread filling in a 1 1/2 to 2-quart gratin dish or other shallow baking dish.
-
23
Pipe mashed potatoes decoratively in mounds on filling and bake in middle of oven until filling is bubbling and potatoes are golden on edges, about 25 minutes.
-
24
Each serving: About 411 calories, 10.7 grams fat (23 percent of calories from fat).
