Step 1 In the bowl of a food processor, combine the fresh and panko bread crumbs along with the parsley, basil, salt and garlic. Pulse the processor to finely chop the herbs. Add the butter and process until evenly combined to form a smooth green butter. Be careful not to overprocess the mixture or the butter will start to melt. Test the seasoning by spreading a little butter on a piece of bread and baking it until crispy and brown; taste, and adjust the seasoning if need be.
Step 2 Remove the butter from the processor and spread between 2 sheets of parchment paper. Roll the butter as evenly as possible; it should be approximately the thickness of two pennies stacked together. In order to achieve uniform thickness, you can use a calibrated rolling pin or roll the butter using a wooden ruler on either side as a guide for thickness (space the rulers far enough apart to allow the butter to expand as it is thinned). Place the rolled butter (still between parchment) on a rimmed baking sheet and freeze overnight before using. The butter will keep, wrapped well, frozen for at least a month and can be used for many things.
Step 3Before finishing the dish, heat the oven to 350 degrees. Shuck the clams and place them on a bed of rock salt in an oven-proof dish. Take the butter from the freezer and remove the top sheet of parchment paper. Cut the butter into rounds using a ring mold or some circular object that is approximately the same diameter as the clams. Remove the bottom piece of parchment from each piece of butter and place one round of butter on top of each clam.
Step 4Bake the clams for 4 minutes, to warm through. Remove the clams and drizzle a couple of drops of garlic oil and fresh lemon juice over each, then finish in the broiler until the butter crust is golden brown and sizzling, 1 to 3 minutes depending on the heat of the broiler. Serve immediately. If you have to cook the clams in batches, bake and broil one batch before starting on the next.