For the stuffing: Over medium heat, melt butter in a heavy bottom skillet until it starts to foam. Add bacon, shallots, and garlic and cook until bacon is cooked and vegetables are translucent, about 6 minutes. Pour in vermouth and stir, scraping bottom of skillet. Reduce heat to low. Add breadcrumbs, Parmesan and parsley. Cook until mixture comes together, approximately 5 to 6 minutes. Remove from heat and set aside.
For the clams: Preheat broiler. Place clams on a sheet tray and place them on the middle rack in the oven. Broil until all of the clams have opened, 6 to 8 minutes. Remove from oven, discard top shells and release clam meats from bottom shells. Add clam "liquor" (juices) to the stuffing.
Spoon about 1 teaspoon stuffing into each clam shell, covering the clam meats. Place clams back in the oven on the middle rack and broil until stuffing is golden brown, approximately 2 to 3 minutes. Garnish with fresh lemon juice and serve.