Ingredients

• 6 tablespoons unsalted butter, divided
• 3 bacon slices, cut into 1/4" pieces
• 2 pounds skinless, boneless chicken breasts or thighs
• Kosher salt, freshly ground pepper
• 3 leeks, white and pale-green parts only, thinly sliced into rounds
• 2 sprigs thyme, leaves stripped
• 1/2 cup quartered pitted prunes
• 1/3 cup all-purpose flour, plus more
• 2 cups low-sodium chicken broth
• All-Butter Pie Dough
• 1 large egg, beaten to blend

Instructions

1. Place a rack in lower third of oven; preheat to 375°. Melt 2 tablespoons butter in a large skillet over medium-high. Cook bacon, stirring often, until crisp, about 4 minutes. Transfer to a plate with a slotted spoon.
2. Season chicken with salt and pepper and cook in same skillet until brown, about 3 minutes per side. Add a splash of water to skillet. Cover, reduce heat, and cook until chicken is cooked through, 10-12 minutes. Transfer to a plate.
3. 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.
4. 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. Let cool.
5. 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.
6. Bake until crust is golden brown, 50-60 minutes. Let pie cool slightly.
7. Do ahead: Filling can be made 1 day ahead. Cover and chill.