Nikkia Rhodes' Chicken Pot Pie

Prepare the Crust: Pulse flour, salt, garlic powder, and onion powder in a food processor until well combined, about 5 pulses. Add cold butter; continue pulsing until butter is pea size, about 10 pulses. Add 4 tablespoons cold water; pulse until incorporated, about 5 pulses. Slowly add up to 6 tablespoons cold water, 1 tablespoon at a time, pulsing until dough just comes together. (You may have to take dough out of food processor and bring it together with your hands. Do not knead the dough.) Shape into a 1-inch-thick disk; wrap tightly with plastic wrap. Chill at least 30 minutes or up to 24 hours.

Prepare the Filling: Heat oil in a large Dutch oven over medium-high. Add onion, carrots, potatoes, and shiitake and portobello mushrooms. Cook, stirring often, until vegetables are tender and beginning to caramelize, 5 to 8 minutes. Add salt, pepper, dried thyme, dried sage, and garlic powder. Continue cooking, stirring constantly, until vegetables are evenly coated, about 1 minute. Add butter, and cook, stirring often, until completely melted. Stir in flour. Continue cooking, stirring constantly, until flour mixture is golden brown and nutty, about 2 minutes. Add stock, milk, and cream cheese; bring to a boil over medium-high, stirring often. Reduce heat to medium. Simmer, stirring often, until thickened, about 10 minutes. Remove Dutch oven from heat, and stir in shredded chicken and spinach; season to taste with salt and pepper.

Preheat oven to 400°F. Grease a 13- x 9-inch baking dish with butter; set aside. Remove and discard plastic wrap from dough. Cut dough disk in half; roll 1 half into a ⅛-inch-thick, 17- x 13-inch rectangle on a work surface lightly dusted with flour. Place dough in prepared baking dish; gently push into bottom and up sides of dish, allowing about 1 inch to extend over sides. (It is okay if it gets a hole in it; just press dough back together.) Add Filling mixture to baking dish. Roll remaining dough half into a ⅛-inch-thick, 10- x 14-inch rectangle. Cut 9 (13- x 1-inch) strips from dough; arrange in a lattice pattern on top of Filling mixture, pressing ends to bottom Crust layer to seal. Trim excess dough from strips; discard. Fold down dough overhang on sides; pinch to seal to lattice strips. Brush dough lattice and border with egg, and sprinkle evenly with flaky sea salt. Bake until Crust is golden and Filling is bubbling, 40 to 45 minutes. Let rest at room temperature 5 minutes before serving.