1To make the filling, heat the stock in a saucepan over medium-high heat with the carrots, celery, and onions. Let simmer until the vegetables are almost tender, about 15 minutes. Turn off the heat and set aside.
2Melt the butter in a large pot or Dutch oven over medium heat. Stir in the flour and cook, stirring constantly, for 2 minutes. Whisk a few ladlefuls of the warm stock into the flour mixture, which will appear lumpy at first but will smooth out as you go. Gradually add all the stock, including the vegetables, stirring as you go. Cook for about 10 minutes, until thickened. During the last minute of cooking, add the garlic and white wine. Remove the pot from the heat and stir in the chicken, peas, tarragon, parsley, salt, and pepper. Taste and add a bit more salt, if desired. Transfer the mixture to a 2½‑ to 3-qt. (2.5- to 3-L) shallow baking dish set on an aluminum foil–lined baking sheet (to catch any spills).
