Whisk the lemon juice and oil. Whisk in the dill and salt.
Heat the butter in a pan. Sauté the onion for approx. 2 mins. Add the lettuce and peas, cook briefly. Pour in the wine and reduce almost completely. Pour in the stock, simmer for approx. 5 mins., blend until smooth. Add the butter and crème fraîche, blend briefly, season. Serve the soup with the dill oil.