Heat butter in a saucepan over medium heat; add onions. Cook and stir until softened, about 2 minutes. Transfer onions to a bowl. Add beef to the saucepan; cook and stir until browned, about 5 minutes. Drain and discard any grease.
Return cooked onions to the saucepan with the beef. Stir in Worcestershire sauce. Sprinkle in flour; cook and stir until slightly browned, about 2 minutes. Remove pan from heat.
Stir beef stock and wine into the saucepan. Return pan to medium heat; cook and stir constantly until mixture boils and thickens, about 5 minutes. Add sliced mushrooms, ketchup, orange juice, coriander, lemon juice, and garlic powder. Reduce heat. Cover and simmer until pie filling is warmed through, about 10 minutes.
Preheat oven to 400 degrees F (200 degrees C). Line a pie plate with 1 crust. Prick the bottom with a fork several times.
Bake in the preheated oven until browned, about 8 minutes. Remove from the oven.
Spoon pie filling into crust and brush the edge with beaten egg. Add top crust and press edges together. Poke several holes in the top crust and brush with remaining beaten egg.
Bake in the preheated oven until golden brown, about 20 minutes.