Fill a large pot with water, bring to a boil. Reduce heat to simmer, add nettles (do not touch with bare hands!); cook and stir for 2 minutes.
Transfer nettles to a colander, let drain. Spread a tea towel on a working surface, transfer the nettles onto the towel, wrap and wring to remove the remaining water.
Add pine nuts, garlic, salt and pepper to a food processor; pulse until finely chopped. Break up the nettles to make them fit into the processor, add lemon juice and pulse again until finely chopped.
Leave the processor on and add oil in a thin streak to let the greens incorporate it. Stop processing when the sauce is smooth. Add cheese and pulse just enough to mix it in, taste, season with more salt and pepper, if necessary, and serve with cooked pasta.