If you've ever had tom yum gai, the hot and aromatic soup that's a mainstay on Thai restaurant menus, then you're already vaguely familiar with yum jin gai, its Northern Thai counterpart. But where tom yum might be Spicy Thai Soups 101, yum jin gai is some serious graduate-level stuff.
Do you remember way back to that seventh time you watched Ghostbusters and you said to yourself, "Holy crap, this just keeps getting better all the time. I'll be damned if I didn't notice a half dozen new layers to this thing that weren't there on the first go around!"
You're all with me on that, right? Because that's what this soup is like. You keep eating and it keeps getting better and better.
Think of the best chicken soup you've had: steaming hot, rich, comforting, and soul-satisfying to the core. Now add to that the complex fragrance of fresh Thai herbs like lemongrass, galangal, and sweet shallots. And wait, we're not done yet! To that base, add a big fat pinch of warm Northern Thai spices—the same blend we used yesterday to flavor our larb muang moo, in fact—and you're starting to get an idea of what it's all about.
The way that Arm, my chef at Small House Thai Cooking taught me, the basic process is extremely simple: boil the fresh herbs in water until aromatic. Add your chicken and cook until tender. Stir in your dried spices, along with mushrooms, shrimp paste, and some herbs. Season to taste and serve.
It works well, but I like to up the chicken flavor a bit more by either making an actual stock out of the trimmed bones of a chicken (cooking the chicken that ends up in the soup at the same time), or by doctoring up store-bought low-sodium broth rather than starting with water.
The spice blend is fairly straightforward: toast dried chile, coriander, cloves, star anise, cinnamon, cardamom, and black pepper, along with some long pepper and some Sichuan peppercorns, then grind it all together.
I find that by then blending this mixture with the shrimp paste and sautéeing it in oil before adding the chicken stock, you get a far deeper flavor and a better texture too.
In Thailand, especially at more rustic restaurants, you'll often get soup served with big chunks of lemongrass or galangal in the bowl. Like bay leaves in Western food, these aren't meant to be eaten. When I make Thai soups at home, I prefer to strain the flavorings out before serving so that you can dig into a bowl without having to worry about picking through it for stray bits of inedible roughage.
But I won't hold it against you if you do it the lazy way.