Step 1: Cook the clams: Fill a large pot with 1 1/2 to 2 inches of water. Bring water to a boil. Add the clams to the boiling water. Reduce the heat to a simmer and let the clams steam for approximately 6-10 minutes, until the shells open. Remove clams from the pot and let cool enough to handle. Discard any clams that have not opened (if they haven't opened it means they were dead to begin with and should not be eaten).
Step 2: Remove the clam meat from the clams (not the clam foot which is attached to the shell) and mince finely.
Step 3: Pick the best clam shells for serving: Break apart the clam shells from their hinges. Rinse. Pick 10-12 of the cleanest, nicest looking clam shells and set aside.
4 Make the stuffing: Preheat oven to 350°F. In a sauté pan, melt the butter on medium heat and add the minced onion. Once the onions have softened (2-3 minutes), add the garlic. Cook the garlic for 1 minute, then add the parsley, bread crumbs, minced clams, lemon juice, and clam juice. Stir until the stuffing mixture is completely moistened. (If too dry, add a bit more butter or clam juice; if too wet, add a bit more bread crumbs.