Make the Khmer yellow herb/spice paste called Kroeung Samlor Machou (see linked recipe above).
Prepare the morning glory by removing old leaves, giving it a thorough wash in clean water, and draining. Coarsely chop the leaves and stems into 3 cm lengths.
If using good quality beef, slice into medium-size pieces that you can eat in two bites.
Combine the beef in the yellow kroeung and marinate for 15 minutes.
Quickly fry the beef and kroeung in the cooking oil in a pan to your taste then transfer to the soup pot.
Add 4 cups of stock to the pot – beef for a meatier taste or vegetable stock for a greener flavour.
Add all the morning glory leaves and half the morning glory stems. Blitz the remainder of morning glory in a blender with a little stock or water, then add to the pot.
Season with the fish sauce and/or prahok, optional tamarind paste (depending on how sour you like your soups), salt, and sugar. Taste. You may wish to add more. If this is your first time making this soup, add half the portions above, taste, then add the remainder if you wish.
Simmer for 30 minutes to retain the green colour and flavour.
Serve with a dish of finely sliced red chillies on the side for guests to add to their taste. These give the soup a nice bite.