Heat a large saucepot over medium heat. Add the chorizo and cook, using a spoon or spatula to break up the sausage into small pieces, until the sausage begins to brown. Add the onions and garlic and sprinkle lightly with salt and pepper. Continue to cook until the sausage has browned, 3 to 4 minutes, taking care not to burn the garlic.
Add the clams to the pot and let settle for a minute, then add the white wine and cilantro. Re-season with salt and pepper and cover tightly with a lid. Let cook about 5 minutes, making sure that the broth at the bottom is at a simmer during that time. After 5 minutes, the clams should have opened or be mostly open; if not, or if the mixture is dry, add another 1/4 cup or so of wine, cover and simmer until the clams are open, 1 to 2 minutes longer. Taste the broth for seasoning and add salt or pepper if necessary. Add the butter to the broth and stir to combine.
Transfer to a large serving bowl, making sure to pour the broth over the clams. (Remove any unopened clams and discard them.) Serve with crusty bread or baguette.
Recipe courtesy of Emeril Lagasse, copyright MSLO Inc., all rights reserved