Begin by preparing the cilantro pesto: pull the cilantro leaves away from their stems. In a food processor or blender, combine the leaves with olive oil, garlic, and jalapeño chile, processing until you achieve a smooth consistency. Add salt and pepper to taste, then set this mixture aside for later.
Warm the oil in a large saucepan over medium heat. Toss in the tomatoes along with the garlic and chili powder, letting everything cook slowly while stirring from time to time. Continue for roughly 8 minutes until the mixture thickens slightly.
Introduce the clams to the pan and stir them around for approximately 1 minute. Next, add the stock and cover the pan with a tight-fitting lid. Let the clams cook over medium heat, giving the pan regular shakes, for 5–8 minutes until they pop open. Remove and discard any clams that remain closed—never attempt to pry them open.
With a slotted spoon, carefully move the opened clams to a warmed serving bowl.
Transfer the remaining cooking liquid to a smaller pan and bring it to a boil, allowing it to reduce by roughly half its volume. Stir in the lime juice and adjust the seasoning as needed, then drizzle this flavorful sauce over the clams.
Present the clams right away, accompanied by fresh lime wedges and the cilantro pesto on the side.
