Slab Chicken Potpie

Combine broth, miso, pepper, salt, thyme and bay leaves in a large saucepan. Bring to a boil over high heat. Cook, undisturbed, until reduced to about 4 cups, about 10 minutes. Discard thyme and bay leaves.

Whisk milk and flour in a small bowl, then whisk into the broth in the pan. Bring to a boil over high heat; cook, stirring occasionally, for 1 minute. Stir in chicken. Remove from heat and let stand for 5 minutes. Stir in mixed vegetables, onions and parsley. Pour the mixture onto a large rimmed baking sheet.

Preheat oven to 425 degrees F.

Unroll pie crusts on a lightly floured work surface, placing one on top of the other. Roll out into a 14-by-19-inch rectangle. Cut into 2-by-19-inch strips using a decorative wheel or pizza cutter. Place half the strips diagonally across the chicken mixture, leaving 2-inch gaps in between. Weave in the remaining strips to form a lattice pattern. Trim excess dough from the edges and discard. Brush the top of the dough with egg. Sprinkle with pepper to taste.

Bake until the top is browned and the chicken is cooked through, 30 to 35 minutes. Let cool for 5 minutes. Cut into 8 pieces.