Soak the beef in cold water for at least 1 hour to remove any remaining blood.

Transfer the beef to a pressure cooker and add 1 head of garlic cloves, skin intact. Pour enough water to cover the beef. Pressure cook for 25 minutes. Discard the cooking liquid and garlic.

Heat a braising pot over medium-high heat. Add a little cooking oil and sauté the mushrooms for a minute. Set aside. In the same pot, add more vegetable oil and sauté the onions and garlic for 2 minutes.

Add the tomato paste and cook for 5 minutes over medium-high heat. Add the chopped tomatoes next and 1/2 cup of the reserved mushroom liquid. Bring to a boil over high heat. Once boiling, reduce the heat to low, season with 1/2 tsp salt, cover, and simmer for 20 minutes. Stir from time to time to mash the tomatoes.

After 20 minutes, add the cooked beef and stir to fully incorporate the sauce. Add 3 Tbsp premium soy sauce and the remaining mushroom liquid. Liquid should total 1 cup. For a saucier filling, add more water.

To make the pastry shell, cut two 3-4 inch circles from the puff pastry sheet. Cut out the center of one circle to create a ring. Place the pastry ring on top of the whole circle and seal the sides with beaten egg whites. Brush the sides lightly with beaten egg. Bake at 350°F / 200°C for 20 minutes, or until golden brown and puffed.

To serve, spoon the mechado into the pastry shell and top with fried potato strings. Serve with roasted vegetables.