There are few foods I find more comforting than a hot soup laced with bracing acid. For years, my stalwarts have been Chinese hot and sour soup, which gets its tang from vinegar, and kimchi jjigae, which picks up its mouth-watering appeal from its namesake pickle. But more recently, I've been craving the brightness of lime as it appears in the tom kha gai and tom yum soups of Thailand.

When I want the real thing, I head over to Pestle Rock in Ballard, but when I'm feeling lazy, I make this. The recipe below is very, very loosely inspired by a creamy tom yum, and combines bright lime juice with creamy coconut milk and sweet, plump shrimp. I often finish it with a drizzle of herb oil, but chili crisp is also a delicious garnish if you're in the mood for something more warming.

Ingredients

For the soup:
3 Tbsp butter
3/4 lb red potatoes, 1/2" diced
2–3 shallots (about 1 1/2 cup, sliced)
3 large cloves garlic, sliced
3 anchovies
1/2 tsp white pepper
1 can full-fat coconut milk
2 cups chicken stock
juice of 1 lime
1/2 lb shrimp, peeled and deveined
watercress oil

For the watercress oil:
2 bunches watercress
1 cup olive oil

Directions

To make the soup, melt butter in a heavy-bottomed pot, then add the shallots and garlic. Cook until fragrant and softened but not browned. Add the potatoes and cook for a few minutes, making sure to coat each piece in the butter. Add in the anchovies, white pepper and 1/2 teaspoon of salt, then stir and cook until the anchovy has dissolved. 

Shake the can of coconut milk well to mix the solids in with the liquid, then add it to the pan, scraping the bottom to unstick any browned bits. Add the chicken stock, then bring it all to a boil. Reduce to a simmer and cook uncovered for 20 minutes, until the potatoes can be easily pierced by a fork but aren’t falling apart. 

Stir in the juice of one lime and taste for seasoning—add more salt as needed. Add the shrimp and cook until bright pink, about 2 minutes.

Dish the soup with shrimp into bowls and drizzle with watercress oil. 

To make the watercress oil, prepare a pot of boiling water and a bowl of ice water. Add the watercress to the boiling water and cook until bright green, about 15–30 seconds. Transfer the watercress to the ice bath to stop the cooking.

When it's cool, squeeze out all the water and add it to a blender or food processor with 1 cup of olive oil. Blend on high for 2–3 minutes. Set a strainer lined with a coffee filter over a bowl and pour the blended oil into it. Let strain for about 30 minutes.