Add the wine, thyme, rosemary, bay leaf, butter, salt and 1/2 cup water to a small Dutch oven. Add the potatoes and bring to a simmer over medium heat. Cover and cook until the potatoes are just cooked through, 15 minutes. Add the lemon slices and clams. Cover and cook until the clams have opened, an additional 3 minutes. Discard any unopened clams. Serve in bowls with a good ladle of the juice and crusty bread for dipping.