Making the paste

Combine the lemongrass in salt and a granite mortar and pound until you have a fairly smooth, slightly fibrous paste, it should take about two minutes.

Add the galangal and pound occasionally stopping to scrape down the sides of the mortar, until you have a fairly smooth paste, about two minutes. Do the same with the turmeric.

Drain the Chiles well, wrap them in paper towels, and gently squeeze them dry. Add them to the motor and pound them, thin the garlic, and then the shallots, fully pounding each ingredient before moving on to the next.

You will have about 1 cup of paste. You can use it right away or store the paste in an airtight container in the fridge for up to one week or in the freezer for up to six months.

Cooking the soup

Combine all of the paste, soy sauce, and chilli powder in a medium pot along with the 8 cups of water and stir well. Add a tablespoon or two of the water to the mortar and pestle and stir to get as much of the paste as you can into the pot.

Set the pot over high heat and bring the liquid to a strong simmer. Add the venison, let the liquid return to a full simmer, then cover the pot and immediately reduce the heat to maintain a gentle but steady simmer. Cook for one hour, then stir in the onions, and keep cooking covered until the beef is tender but not falling apart and the broth has thickened slightly (about 1 to 1 1/2 hours more).

Season to taste with salt. Tear the lime leaves by hand and add them to the pot along with the black pepper. Turn off the heat and let the dish cool slightly. Right before you serve it sprinkle on the herbs and spring onions.

This dish is best served with Thai sticky rice, but you can use steamed rice or even add noodles (although not authentic) if you wish.