Step 1: Make the chile sauce

First, heat a large pot over medium heat. Add the guajillo, cascabel, and chile de arbol (if using) and dry toast them for 1-2 minutes. Keep an eye on them and flip halfway through – they should become fragrant but not burnt. Once toasted, transfer the chiles to a food processor or blender and pour in 2 cups of hot water. Let them sit for about 20 minutes until they soften completely.

In the same pot, add 1 tablespoon of vegetable oil over medium heat. Sauté the chopped onion for 4-5 minutes until it becomes soft and translucent. Then, add the chopped tomato and cook for another 5 minutes, letting it break down and release its juices. Finally, toss in the garlic and cook for just a minute – you’ll know it’s ready when you can smell the garlic’s fragrance.

Add the softened chiles and the onion-tomato mixture to your blender. Blend until the sauce is smooth. You may need to add a splash of water if it’s too thick. Set this sauce aside for now.

Step 2: Make the shrimp stock

Now it’s time to make the shrimp stock, which gives this soup an extra depth of flavor. In the same pot, heat another tablespoon of oil over medium heat. Add the reserved shrimp shells (and heads if you have them) and cook for about 5 minutes. Stir them around to release all the shrimp flavor – you’ll notice the shells turning a vibrant pink.

Once the shells are nicely cooked, add 4 cups of water to the pot. Bring it to a simmer and let it cook for about 5 minutes, pressing down on the shells with a spoon to extract as much flavor as possible. Strain out the shells and discard them, keeping the stock in the pot.

Step 3: Combine the soup

Pour the chile sauce into the pot with the shrimp stock. Stir well, then add the diced potatoes, carrots, dried epazote (or cilantro), bay leaf, and a generous pinch of salt and pepper. If you want a brothier soup, add an extra cup of water. Cover and let it simmer for 15 minutes, or until the vegetables are tender.

When the vegetables are ready, add the shrimp to the pot. Cover and simmer for just 2-3 minutes, or until the shrimp turn pink and are cooked through. Overcooking the shrimp can make them rubbery, so keep a close eye on them!

Finally, stir in the juice from two limes and remove the bay leaf. Give the soup a taste and adjust the salt and pepper if needed.