2 lbs whole chicken breasts with skin and bones
1 cup pearl onions, unpeeled
2 Jersey Fresh medium carrots, cut into 1/4-inch thick slices
2 Jersey Fresh celery ribs, cut into 1/4-inch thick pieces
1/2 cup Jersey Fresh peas
1/4 pound mushrooms, sliced thin
2 tablespoons unsalted butter
1/4 cup Jersey Fresh shallots, finely chopped
1 bay leaf
1/4 teaspoon Jersey Fresh thyme, crumbled
1/4 teaspoon Jersey Fresh tarragon, crumbled
1/4 cup all purpose flour
1/3 cup Jersey dry white wine
2 1/2 cups chicken broth
salt and pepper to taste
For Mashed Potatoes:
1 1/2 pounds Jersey Fresh potatoes
1/4 cup sour cream
3 tablespoons Jersey Fresh chives, minced
salt and pepper to taste
To make filling: In a large saucepan, bring 3 quarts of water to a boil. Add chicken and simmer, uncovered 25 minutes.
Remove pan from heat and transfer chicken to a bowl, discarding cooking liquid. Cool.
Discard skin and bones. Cut chicken into 3/4-inch cubes.
Bring 2 quarts water to a boil and cook onions until tender. Transfer onions to a bowl of cold water, reserving cooking liquid in pan. Peel onions and add to chicken. Return reserved cooking liquid to a boil and cook carrots and celery until just tender. Drain carrots and celery and add with uncooked peas to chicken mixture.
Cook mushrooms in 1/2 tablespoon butter over moderate heat, stirring, until softened and golden brown and add to chicken mixture.
Cook shallots with bay leaf, thyme, and tarragon in remaining 1 1/2 tablespoons butter over moderately low heat, stirring, until soft and pale golden and stir in flour. Cook mixture, stirring, 3 minutes and gradually whisk in wine, broth, salt and pepper to taste. Simmer sauce 5 minutes, whisking occasionally.
Discard bay leaf. Pour sauce over chicken mixture and stir until combined well.
For Mashed Potatoes: Peel potatoes and cut into 1-inch pieces. Cover potatoes with water and simmer until very tender. Drain potatoes and reserve about 1/3 cup cooking liquid. In batches, force potatoes through a ricer or food mill fitted with medium disk into a bowl and stir in sour cream, chives, salt and pepper to taste, and enough reserved cooking liquid to reach a fluffy consistency. Do not use a food processor. Transfer potatoes to pastry bag filled with a 1/2-inch fluted tip.
Spread filling in a 1 1/2 to 2-quart gratin dish or other shallow baking dish. Pipe mashed potatoes decoratively in mounds on filling and bake in a pre-heated 425° oven until filling is bubbling and potatoes are golden on edges, about 25 minutes.