I use Western littleneck clams for this recipe because that's what I can forage for here in NorCal. You could use any small hard-shell clam, and Manila or Eastern littlenecks are just as good or even better than then Western clams I use.
Lay the clams in a wide pan, like a big frying pan, in one layer; you may need to do this batches. Pour 1 cup of white wine in the pan and turn the heat to high. Cover the pan and steam the clams open. Keep an eye on the pan and check every minute or two and remove each clam as soon as it pops open. Move the opened clams to a bowl. Keep doing this, adding and removing clams, until they are all opened. Tap on the shells of those clams that don't seem to want to open, and sometimes they'll pop. If they stay resolutely closed, toss them.
Your choice here: I remove all but a few of the clams from their shells because it's easier to eat this way; I leave a few clams in the shells for garnish. Some people just like to pick through the whole shebang, and if you're one of those, go for it.
OPTIONAL: Strain the clam juice through a paper towel to remove grit. You can use this for the finished dish.
Wipe out the pan you cooked the clams in and heat the olive oil over medium-high heat. When it's hot, sauté the onions until they are soft and the edges have browned a bit. Add the chiles, garlic and chorizo and cook for another minute or two.
Crumble the saffron over the pan and sprinkle the paprika over everything. Add the remaining white wine, the clams and enough of the strained clam juice (or water) to halfway cover everything. Boil this furiously for about 90 seconds. Turn off the heat, add the lemon juice, chopped herbs and black pepper. Serve at once with a big loaf of crusty bread.
I like to eat this with good bread and a dry rose or a very light red, like a Spanish Garnacha, California Gamay or French Beaujolais. Hard cider is another good choice here, as would a full-flavored white wine like a Portuguese Verdelho.