Tom Kha Soup (Thai Coconut Soup with Shrimp or Chicken)

Why galangal leads the flavor in tom kha

Kha means galangal, so the name tells you what the soup should taste of. Galangal looks like ginger with a paler, tougher skin, but its flavor is sharper and more piney, almost citrusy, with less of ginger's sweet heat. Slice it thin and let it steep in the coconut milk with the lemongrass and lime leaves for 8 to 10 minutes before anything else goes in.

Ginger works as a stand-in; use the same amount. The soup will still be good, just warmer and less perfumed. The other aromatics have their own substitutes:

• Makrut lime leaves: the zest of 1 lime, removed in wide strips, gives some of the perfume. There's no exact match.
• Fresh lemongrass: frozen lemongrass or lemongrass paste in a tube (about 1 tablespoon per stalk).
• Palm sugar: light brown sugar, measured the same.
• Bird's eye chiles: 1 serrano, or a pinch of red pepper flakes.

Asian grocery stores sell galangal, lemongrass and lime leaves fresh or frozen. All three freeze well for months, so it's worth buying extra.

Tom kha vs tom yum

Both are classic Thai soups built on lemongrass, makrut lime leaves, lime and chile, and people often mix them up. Tom kha puts galangal in front, in a broth made rich with coconut milk. Tom yum is usually hot and sour first, with a thinner broth.

This recipe is the milder, creamier of the two. If you want it closer to tom yum, add a tablespoon of Thai chili paste (nam prik pao) with the mushrooms and an extra tablespoon of lime juice at the end.

Which protein: shrimp, chicken or tofu?

Shrimp is the version written here, known in Thailand as tom kha goong. Chicken, tom kha gai, is the one most restaurants serve. Either goes in near the end, after the broth has taken on the aromatics.

• Shrimp: 3 to 4 minutes in simmering broth, until pink, opaque and curled into a loose C. A tight O means they've gone rubbery. The USDA safe temperature chart lists 145°F for shellfish.
• Chicken: slice boneless breast or thigh thinly and simmer 5 to 6 minutes, until it reaches 165°F.
• Tofu: 14 ounces (400 g) pressed and cubed, with vegetable stock and light soy sauce in place of fish sauce, for a vegetarian bowl.

Seared scallops are another good swap. Cook them separately in a very hot pan, as in these pan seared scallops, and set them in the bowls just before ladling the soup around them so the crust stays crisp.

When should the fish sauce and lime go in?

Last, with the pot off the heat. Fish sauce and lime juice both lose their fresh edge when they boil, and the lime in particular goes flat. Thai cooking treats seasoning as a balance you adjust at the end rather than a fixed measurement, because limes vary in sourness and fish sauces vary in saltiness.

Stir in the fish sauce, palm sugar and lime juice, taste a spoonful, then adjust one thing at a time:

• Tastes flat or thin? Add fish sauce, 1 teaspoon at a time.
• Tastes heavy or too rich? Add lime juice.
• Too sharp or salty? A pinch more palm sugar rounds the edges.
• Not lively enough? Crush another chile into the pot and let it sit for a minute.

Stop when no single flavor jumps out ahead of the others.

Keeping the coconut broth smooth

Coconut milk splits when it boils hard, leaving oily streaks and a grainy broth. Keep the pot at a gentle simmer with small bubbles at the edges, and use full fat coconut milk, since light coconut milk makes a thin broth that separates more easily. If it does split, whisking off the heat usually brings it back, and the flavor barely changes.

In Thailand this soup is part of a shared meal, eaten alongside rice and other dishes rather than as a course of its own. Steamed jasmine rice is the simplest partner; spoon some into the bowl or alternate bites. Served in small cups, it also works as a light starter before a spiced main like butter chicken, and a crunchy cucumber salad with rice vinegar is a cool contrast to the creamy broth.