Sorrel, Radicchio, and Romaine in Creamy Parmesan Dressing

A creamy, salty sauce mellows and coats tart sorrel, bitter radicchio, and sweet romaine. The dressing yield is about double what is needed for this quantity of “greens” (a range of exceptionally lively hues and varied textures), but that’s what one egg makes. You can: double the greens and use all the dressing, to serve eight; halve the egg and make just half the dressing; or refrigerate the unused dressing to spoon over grilled or baked fish or steamed potatoes. If you are concerned about