Wash the clams by agitating them in a bowl of cold water. Pour off the dirty water and cover the clams in clean, cold water for at least 15 minutes, or up to an hour, while preparing the rest of the ingredients. This will help the clams spit out (purge) some of the sand that is in their digestive system.
Cut the chorizo into a small dice (1/4 inch).
In a pot with a lid that will comfortably hold the clams, heat up 1/2 Tbsp of olive oil over medium-high heat. Add the diced chorizo and cook for about 45-60 seconds, or until starting to change color and the fat begins to render into the olive oil.
Add the garlic and sliced shallot to the pan.
Cook the garlic and shallots while stirring for about one minutes or until they start to soften up but are not browning
Drain the clams from the water they were soaking in and add them to the pot along with the butter and white wine.
When the wine comes up to a simmer, immediately put the lid on the pot and turn the heat to medium. Cook the clams at a simmer for about 4-7 minutes, or until all of the clams have opened up.
Check to make sure all of the clams have opened up. If you notice a clam open and it is full of mud, carefully discard it as soon as possible before it contaminates the broth. If there is an off-smell coming from the pot, one or more of your clams may have been bad, try to isolate and discard them if possible.
Add the lemon juice and parsley/cilantro to the clams and give them a quick stir.
Serve with warm, crusty bread