Put clams into boiling water, oven and steam until they open. Discard any that do not open. Take the clams out of their shells. Save the bottom shell and the cooking water. Chop the clams.
Sauté the bacon, until crispy, remove and chop. Sauté the chopped onion and garlic in the bacon fat, add the butter and once hot, the breadcrumbs, the chopped bacon the seasonings and the chopped clams. Stir until well mixed and take off the heat. Add the lemon juice and if the mixture is too dry, add a little of the cooking water.
Pack the mixture into the bottom shells and place on a cookie sheet. If the shells do not lie flat you can put them on a bed of sea salt which stops them from wobbling. Bake in the oven at 350ºF for 10 minutes.