Chop the new leeks (in this case, since they are new, I keep the dark green part).Melt the butter in the sauté pan. Pour in the oil and sweat the onion.When it is translucent, add the leeks and let them fall quietly over low heat.Cover if necessary. They must not brown!Pour in the white wine and season. Let it simmer over low heat until tender.A great accompaniment to meat or fish, leeks are delicious and can be served as a garnish or as a side dish.