In your blender jar, add the garlic, shallots, ginger and candlenuts. Blitz into a fine paste, then set aside until ready to use.
In a large skillet over medium high heat, heat the oil. When the pan is hot, sear the beef cubes in batches, until browned, about 1 minute per side. Remove from the pan and add to your pressure cooker pot.
In the same pot, add the cinnamon, star anise, cloves, and cardamom pods. Cook, stirring, until spices are fragrant, about 1 minute.
Add the blended ingredients and cook, stirring, until the liquid has evaporated, 1 to 2 minutes.
Add the soup spice mix and 1 tablespoon ground black pepper and cook, stirring, until spices are fragrant, about 1 minute.
Add some water to the pan and scrape off any bits from the bottom. Pour the contents of the pan into your pressure cooker pot, along with the remaining water.
In your pressure cooker pot, add the lemongrass, the white part of the green onions, the sup bunjut pouch, the Thai chili, and the dates if using.
Close and lock the pressure cooker lid and cook at high pressure, 30 minutes. When done, let the pressure cooker depressurize and carefully remove the lid.
Turn on the Sear function on your pressure cooker, and return the mixture to a boil. Add the potatoes, celery and carrots and cook, until potatoes are tender, 12 to 15 minutes.
Season with the beef stock cube, seasoning powder, salt, remaining 1 teaspoon black pepper and mushroom powder if using. Adjust to taste.
Garnish with the chopped green parts of the green onions, and fried shallots.
Serve hot, with steaming hot white rice. Squeeze a wedge of lime if desired, to add a little brightness to the soup.