Step 1

Heat a large pot or Dutch oven to medium heat. Add the guajillos, cascabel, and chile de arbol. Dry toast them in the pot for 1-2 minutes, flipping them halfway through, until lightly toasted and fragrant.

Step 2

Add the chilies to a food processor or blender and cover with 2 cups hot water. Cover for 20 minutes, until the peppers are very soft.

Step 3

Heat 1 tablespoon oil in the same pot over medium heat. Add the onion and cook for 4-5 minutes to soften.

Step 4

Add the tomatoes and cook for 5 minutes, or until the tomato is broken down.

Step 5

Add the garlic and cook, stirring, for 1 minute, or until the garlic becomes fragrant.

Step 6

Add the mixture to the food processor with the softened peppers. Process until smooth.

Step 7

Chop the reserved shrimp shells (and shrimp heads, if using).

Step 8

Heat 1 tablespoon oil in the same pot over medium heat. Add the shrimp shells (and shrimp heads, if using). Cook for 5 minutes, stirring.

Step 9

Add 4 cups water. Bring to a simmer and simmer for 5 minutes, pressing the shrimp shells down a bit to squeeze out their flavor. Strain out the shells and discard them.

Step 10

Strain the chili sauce from the food processor into the pot with the shrimp broth, then add the potatoes, carrots, epazote, bay leaf, salt and pepper to taste. For a soupier broth, add 1 extra cup of water. Cover and simmer for 15 minutes, or until the vegetables are softened to your liking.

Step 11

Add the shrimp and cover. Simmer 2-3 minutes, or until the shrimp cook through.

Step 12

Stir in the lime juice and remove the bay leaf.

Step 13

Serve with extra limes and cilantro for garnish.