Scrub the clams and rinse them clean. Add 7 cups of water to a large stockpot fitted with a steamer basket or colander, and bring to a boil. Add half the clams to the basket and cover. Steam until the clams open, 5 to 10 minutes. (Discard any clams that don’t open.) Repeat with the second batch of clams. Reserve 6 cups of the broth. Set aside. Cool the clams; remove the meat from the shells and dice it into ½-inch pieces. Keep them covered and refrigerated until ready to use. Put the bacon in a 5- to 7-quart pot over medium heat. Cook, stirring occasionally, until golden brown, about 10 minutes. Pour off all but 1 tablespoon of the bacon fat, leaving the bacon in the pot. Reduce the heat to medium-low. Add the butter, onions, celery, and bay leaves, and cook, stirring occasionally, until the onions are softened but not browned, 6 to 8 minutes. Add the potatoes and reserved clam broth to the pot. Continue cooking over medium heat until the chowder begins to simmer. If it begins to boil, reduce the heat slightly. Cook until the potatoes are tender, about 15 minutes.  Just before serving, remove the pot from the heat, stir in the clams and herbs, discard the bay leaves, and season to taste with salt and pepper. Serve hot. Steaming the clams might seem laborious, but it’s actually easy and makes a briny broth. Aim to extract 6 cups of broth from the clams; if not, you’ll need to have some bottled clam juice on hand to round it out.