Layers of flaky filo dough on top of this chicken pot pie transform the comfort food classic from the everyday to the elegant. Serve each portion with a filo triangle on top so there is some of the crispy dough in every bite.
To make the filling, during a 5-quart Dutch oven over medium heat, melt the butter. Add the flour and cook, stirring constantly, until the mixture smells fragrant and nutty, about 2 minutes. Whisk within the Madeira and demi-glace. Slowly add the chicken broth , whisking until smooth, and convey to a boil. Add the diced onion, celery, mushrooms, thyme, tarragon and herb and cook until the vegetables are almost tender, about 10 minutes. Add the potatoes, chicken and pearl onions and season with salt and pepper. Cook until the potatoes are tender, about 10 minutes. Remove from the warmth and let cool for 10 minutes. Remove the herb and discard.
To assemble the pot pie, on a dry surface , gently unroll the filo. Cut the phyllo in half horizontally. Cover half the filo with a rather damp towel and put aside .
Spread 1 filo sheet from the second stack on your surface and, employing a pastry brush, lightly brush with melted butter. Cover with a second sheet, rotating it clockwise slightly, and brush it with more butter. Repeat with the remaining sheets from the second stack, rotating all slightly and brushing each with butter. Carefully lift the stack of buttered filo and place it on top of the pot pie, folding the dough up as necessary along the sides of the pot. Brush the filo with the egg wash and sprinkle with sea salt.
Bake until the filo is crisp and browned everywhere , 15 to twenty minutes, covering the sides of the filo with
aluminum foil about halfway through the cooking time if necessary to stay them from turning too brown. Remove from the oven and let cool about 10 minutes before serving.
While the pot pie is cooking, prepare the remaining filo. Spread 1 of the remaining filo sheets on your surface and, employing a pastry brush, lightly brush with melted butter. Cover with a second sheet and brush it with butter. Repeat with the remaining sheets of filo, brushing each with butter. employing a sharp knife, cut the sheet of filo into 8 triangles of equal size. Transfer the triangles to the prepared baking sheet.
While the pot pie is cooling, place the filo triangles within the oven and bake until lightly browned and crispy, 8 to 10 minutes.

Chicken Pot Pie with Mushrooms and Thyme
For the filling:
- 14 Tbs. (1 3/4 sticks) (7 oz./220 g) unsalted butter
- 1 cup (5 oz./155 g) plus 2 Tbs. all-purpose flour
- 1⁄3 cup (3 fl. oz./80 ml) Madeira
- 2 Tbs. chicken demi-glace
- 7 cups (56 fl. oz./1.75 l) chicken stock
- 1 large yellow onion, diced
- 4 celery stalks, sliced 1/8 inch (3 mm) thick
- 1 lb. (500 g) cremini mushrooms, trimmed, brushed clean and thinly sliced
- 1 Tbs. chopped fresh thyme
- 2 tsp. chopped fresh tarragon
- 1 bay leaf
- 8 oz. (250 g) small red-skinned potatoes, cut into 1⁄2-inch (12-mm) dice
- 8 cups cubed cooked chicken (about 3 lb./1.5 kg total)
- 1 bag (1 lb./500 g) frozen pearl onions
- Salt and freshly ground pepper, to taste
For assembling:
- 1 box (1 lb./500g) filo dough, thawed if frozen
- 8 Tbs. (1 stick) (4 oz./125 g) butter, melted
- 1 egg beaten with 1 tsp. water
- Sea salt, to taste
Preheat an oven to 400°F (200°C). Line a baking sheet with parchment paper.