Heat 2 tablespoons of olive oil in a large saucepan over medium heat and brown the beef stew meat on all sides, about 10 minutes; set aside. Heat the remaining 1 tablespoon of olive oil then cook the bacon just until it begins to brown; stir in the onion, carrot, mushrooms, garlic and sugar. Cook the vegetables until soft and browned, 10 to 15 more minutes.
Stir in the flour until smoothly incorporated then gradually mix in the stout beer and beef stock. Mix in the thyme, bay leaves and the reserved cooked beef. Cover and bring the mixture to a boil; reduce heat to a simmer until the meat is tender, about 1 hour and 15 minutes; stir occasionally. Remove the cover, turn the heat up to medium and let the stew boil until slightly thickened, about 15 more minutes. Mix cornstarch with water and stir into the stew; let simmer for 30 more minutes to blend flavors. Remove from heat; discard bay leaves.
Preheat oven to 180 degrees C.
Spread the filling into a 23cm pie dish; trim the puff pastry into a larger circle and place on top of the filling. Pinch and crimp the edges of the pastry with a fork, sealing it to the dish; cut 2 steam vents into the pastry with a sharp knife. Brush the top of the pie with beaten egg.
Bake in the preheated oven until the crust is browned, 30 to 40 minutes.