Cock-a-Leekie Pie

Add a splash of water to skillet.

Cover, reduce heat, and cook until chicken is cooked through, 10-12 minutes.

Transfer to a plate.

Add leeks to skillet, season with salt and pepper, and cook, stirring often, until softened, about 5 minutes.

Add a splash of water, cover, and cook until leeks are very soft, 5-7 minutes.

Transfer to a large bowl.

Shred chicken and add to leeks along with thyme leaves and prunes.

Melt remaining 4 tablespoons butter in a medium saucepan over medium-high heat.

Whisk in 1/3 cup flour and cook, whisking constantly, until golden brown, about 3 minutes.

Whisk in broth, adding a little at a time, until smooth.

Simmer, stirring occasionally, until thickened, 5-7 minutes.

Mix sauce into leek mixture; season with salt and pepper.

Roll out 1 disk of dough on a lightly floured surface to a 14" round.

Transfer to a 10" cast-iron skillet or a 9 1/2"-diameter deep pie dish.

Lift up edge and let dough slump down into dish.

Trim, leaving a 1" overhang.

Spoon filling into skillet.

Roll out second disk of dough to 11" round.

Drape over filling and trim to a 1" overhang.

Fold overhang under; crimp with a fork.

Cut a few vents in top; brush with egg.

Bake until crust is golden brown, 50-60 minutes.

Let pie cool slightly.

Do ahead: Filling can be made 1 day ahead.

Cover and chill.