In a  STAUB® 4-quart Cast-Iron Cocotte, melt 1/2 cup of the butter over medium-low heat. Add the flour and whisk well. Add the Madeira, stir well, and bring to a boil. Add the onion, celery, carrot, potatoes, bay leaf, and curry powder. Season with salt and pepper. Cover and cook until the vegetables are tender, 8 to 10 minutes. Remove the bay leaf and add the chicken and peas. Remove from the heat.

In a small fry pan, melt the remaining 1/2 cup butter over medium-low heat. Remove from the heat.

Spread the phyllo dough onto a clean surface and cut in half crosswise. Return half of the pyllo to the freezer and save for another use. Place one piece of the remaining phyllo on the countertop. Using a pastry brush, brush the melted butter over the phyllo. Top with another piece of phyllo, placing it slightly off center to create the start of a star shape. This will make it easier to place on top of the cocotte. Repeat with the remaining sheets of phyllo.

Carefully pick up the phyllo and transfer it to the cocotte. Press the phyllo into the cocotte, keeping an overhang of phyllo on the sides of the pot. Brush the phyllo with the egg wash and carefully slice a slit in the top of the phyllo. Bake the chicken pot pie for 25-35 minutes, until the phyllo is golden brown.

Let the chicken pot pie rest for 10 minutes then serve warm.