Begin by searing the seasoned beef cubes in a pot over medium-high heat until browned, about 5-7 minutes. Once browned, remove the beef and set it aside to keep its juices.

In the same pot, add diced onions and mushrooms. Sauté until soft and fragrant, around 5 minutes. Stir in the flour and tomato paste, cooking until the mixture darkens slightly.

Pour in the Guinness, scraping the bottom of the pot to release any delicious browned bits. This should take about 2 minutes. Return the browned beef to the pot, mixing it with the vegetables.

Cover the pot and simmer the beef on low heat for around two hours until fork-tender.

Let the filling cool for about 30 minutes to meld the flavors before assembling your pot pie.

Roll out your pie crust or puff pastry according to the size of your pie dish or ramekins, aiming for a thickness of about 1/8 inch.

Fill your pie dish or ramekins with the hearty beef mixture, then cover it with the pastry. Pinch the edges together to seal.

Brush the top with the egg wash for a golden finish, then bake at 400°F for 30 to 40 minutes, or until the crust is beautifully golden and the filling is bubbling.