Source (timestamp: 0:37)
Brown shallots/onions in a saucepan. Add tomato with a small amount of water, to deglaze the pan and help the tomato soften. Stir until it's a sort of mash. If you're making a single serving of soup, set aside ~2 thirds of the shallot-tomato base to use for other dishes. (Or don't. Use as much as you want.)
Add desired amount of water to your shallot-tomato base. Add fish sauce, pepper, MSG, and chicken bouillon powder and tamarind concentrate if you're using (plus whatever other seasonings you want). You'll know you've seasoned your soup correctly when you taste it and it makes your mouth happy.
This is when I would also add the baby shrimp. They only take about a minute to cook.
In the original video, Uyen cracks her eggs directly into the pot and stirs it quickly to encorporate. I personally like to whisk my eggs in a separate bowl, then slowly pour them into the soup while stirring, to get delicate egg ribbons. Use whichever method you prefer.
This is now when I would add in my spinach. I push it into the soup until it has just wilted to avoid overcooking astringency.
Add green onion. Transfer to your eating vessel, drizzle with sesame oil if you're using. Uyen also recommends adding corriander, but I have yet to try this.
Uyen recommends eating with rice, or mixing it with pasta (but only if you don't tell anyone she said that). I recommend pairing it with a milk tea of your choice, as the sweet creamy taste nicely balances out the rich savoury soup.