1Bring 2 cups water to boil in a large pot. Add clams, reduce to simmer and steam clams 10 minutes. Preheat oven to 350.
2Remove clam meat and mince. Break shells at hinges and clean.
3If using raw bulk spanish chorizo, brown it in frying pan. Remove to plate. Saute onions in butter until soft, then add garlic. Cook one minute, then add parsley, clam water, lemon juice, bread crumbs, minced clams, and sausage. Cook 4-5 minutes.
4Lay clams shells on cooking sheet. Put spoonful of stuffing on each shell. Sprinkle with Parmesan cheese. Bake 20-25 minutes. Serve with a lemon slice.