Tom Kha Gai (ต้มข่าไก่)

The Soup Named After Its Herb

Tom kha gai is the only Thai soup named after an ingredient: ข่า (kha), the galangal. Its gentle heat — lighter than ginger, more floral than lemongrass — defines the whole dish. R-HAAN, the two-Michelin-star restaurant whose chef feeds the world's leaders, calls it "a poem of flavour": coconut milk's richness, galangal's soft heat, lemongrass and makrut's fragrance, lime's fresh sour, all in balance. It moved from royal court tables to every home kitchen in the country.

And Thai cooks are protective of it. On Pantip, when a home cook asked when to add lime so her milk version wouldn't split, the replies came back in verse: "The real thing must be coconut milk. Don't be weird and add milk — bitter and sad." The dairy version is not a variation; it's a different soup.

The Recipe (R-HAAN quantities, Mahidol method — serves 3–4)

The Method

1. Start the milk. Coconut milk in the pot over medium-low, stirring constantly at first so it can't separate. Galangal, lemongrass, makrut leaves and bruised shallots go in, and the herbs release their flavour slowly into the milk.
2. Poach the chicken. Once the milk is fragrant, the chicken goes in. Gentle heat, no hard stirring — the soup stays white and silky. Cook until just done.
3. Mushrooms and salt. Straw mushrooms in, then fish sauce and a little salt. Taste — the salty line comes first.
4. The cream, late. Coconut cream stirred in over low heat once the chicken is tender. Never let it boil hard — that's how coconut milk splits and turns greasy.
5. Off the heat: lime and chillies. Pot off the stove, then lime juice and bruised chillies. Boiling turns lime bitter — this order is the difference between fresh-sour and flat. For the old-style soft sour, swap the lime for tamarind water, which can go in during cooking.
6. Finish. Coriander leaves on top, serve hot with jasmine rice. Eat it hot — cold tom kha is greasy and muted (Mahidol's serving tip).

Where Thai Sources Disagree

How Western Versions Get It Wrong

• Dairy milk. The defining error — "cream of chicken with coconut flavouring" soups. Thai home cooks mock it in verse. Coconut milk is the dish.
• Ginger instead of galangal. They are not interchangeable. Ginger is hotter and sharper; galangal is piney and cool. If it tastes of ginger tea, it isn't tom kha.
• Lime while boiling. Heat destroys lime's freshness and turns it bitter. Off the heat, always — or use tamarind for the cooked-in sour.
• Hard boil. Boiling coconut milk splits it into curds and oil. The soup is poached, not boiled.
• Nam phrik phao as "the authentic secret." It's a modern addition, fine as a garnish, but the classic has no chilli paste.

UK Ingredient Notes

• Galangal: fresh or frozen in Asian grocers, sold in fingers. Young galangal is hard to find here — standard galangal sliced paper-thin works; just don't eat the slices.
• Never substitute ginger. If you can't get galangal, make something else.
• Coconut milk: use a full-fat tin. For the milk/cream split, shake and use the thin part as the base, the thick part (or a second tin's cream) as the late addition.
• Makrut lime leaves: fresh in Asian grocers, frozen as backup. Midrib out before tearing.
• Straw mushrooms: fresh in Asian grocers; tinned ones work but rinse them.
• Bird's eye chillies: anywhere. Bruise, don't slice — you want heat in the soup, not seeds everywhere.

Sources

This recipe is translated from the following Thai-language sources. Where they disagree, we've said so.