Wearing gloves and using scissors, harvest fresh nettles by cutting leaves into basket, avoiding brushing plant with bare skin. Coarsely chop nettles in a food processor; if chopping by hand, wear gloves to protect against stinging. Melt butter in large saucepan, then add oatmeal and cook 5 minutes to toast it slightly. Add stock and bring to boil, then add milk if using. Bring back to boil.
Add nettles and cook 10 minutes on high. Add seasonings and serve immediately, adding a dollop of sour cream if desired. Reheats well; simmer gently on stovetop to reheat.
Irish variation: add two diced potatoes to stock, cook until soft, puree before adding nettles.
Cornish nettle soup: cut up one link sausage per person; add to soup and warm thoroughly before serving.
Scottish nettle soup: simmer one each minced onion and carrot in butter; add stock and continue as above. Garnish with chives.