Heat the oven to 350ºF.

• Peel the shallot and cut into thin slices.
• Finely chop the garlic.
• Cut the top off the serrano (if using), cut in half lengthwise, remove the ribs and seeds, and then cut into thin strips.
• Finely chop the cilantro.
• In a mixing bowl, whisk the eggs.

Tear the ciabatta into 1-inch pieces and spread on a sheet pan in an even layer. Drizzle with oil, season with salt and pepper, and toss to coat. Toast in the hot oven until golden brown, 10 to 12 minutes. While the bread toasts, prepare the soup.

In a pot over medium-high heat, warm 2 tablespoons oil until hot but not smoking. Add the shallots, season with salt, and cook until softened, 3 to 4 minutes. Add the garlic, as much of the serrano as you like, and the spice blend, and cook until fragrant, 1 to 2 minutes. Add the shrimp, chicken stock, and 2 cups water. Bring to a boil, reduce to a simmer, and cook, stirring occasionally, until the shrimp is pink and cooked through, 2 to 3 minutes longer. Remove ½ cup of the broth from the pot and slowly add it to the bowl containing the eggs, whisking to combine. Slowly stir the egg mixture back into the soup. Add the cilantro, and season with salt and pepper.

Transfer the croutons to individual bowls, ladle the soup on top, and serve. (For crispier croutons, serve them on the side.)