Thoroughly clean the clams.
Place the vegetables, peppercorns, parsley and fish stock in a saucepan that has a tightly-fitting lid and bring to the boil. Once boiling, add the clams, cover with the lid and boil until they open, about 4-5 minutes. Drain and save the liquor, allow the clams to cool, then remove them from their shells.
Wash the nettle leaves well and put 18 nice leaves to one side. Roughly cut the bacon into pieces. Melt the butter in a saucepan, add the shallots, garlic and bacon and sweat until the shallots start to soften. Add the nettles, continue sweating for a further 2 minutes, then pour in the clam liquor. Bring to the boil and simmer gently for 15 minutes. Strain the soup, put the liquid to one side and blend the solids in a food processor or blender until smooth. Return them to the liquid and then strain again.