Cook the bacon in a medium skillet over medium heat until crisp. Drain and chop fine. Set aside.
In a small bowl, stir together the butter, shallots, garlic, parsley, lemon juice, salt, and cayenne until combined. Set aside.
Arrange the clams in a single layer in a large skillet pan, cover, and steam over high heat until their shells just begin to open, about 5 to 8 minutes. (Do this in batches if needed.) Set aside. When cool enough to handle, remove the top shells and discard. Slide a knife under each clam to loosen it in the shell.
Crumple a large piece of aluminum foil and spread it out on a baking sheet. (The creases in the foil help keep the clams from tipping over.) Spread about a 1/4 teaspoon of the seasoned butter on top of each clam, top with some of the bacon, and about 1/2 teaspoon of the crumbs. Evenly space the clams on the prepared baking sheet. (The clams can be prepared to this point, covered, and refrigerated, up to 4 hours before serving.)
Place a rack about 4 inches from the broiler element and preheat. Broil the clams until the crumbs are toasted and the butter is sizzling, about 3 to 4 minutes. Serve warm.