sherry wine vinegar
extra-virgin olive oil
mâche (loosely packed)
head of frisée (halved, torn into pieces, about 6 cups, loosely packed)
head of Chioggia, Tardivo, or Castelfranco radicchio (halved, torn into pieces, about 5 cups, loosely packed)
red onion (sliced thinly, about 2 cups)
Kalamata olives (pitted and halved)
feta cheese (crumbled)
Salt and freshly ground pepper (to taste)
To make the dressing, cut the peel and white pith from the oranges. Working over a small bowl and using a small, sharp knife, cut between the membranes to release the segments. Squeeze membranes to release the remaining juice. Combine 1/4 cup orange juice and vinegar in a small bowl (reserve remaining juice for another use). Whisk in olive oil. Season to taste with salt and pepper.
Toss the mâche, frisée, and radicchio in a large bowl. Add the orange segments, onion, and olives. Drizzle dressing over the salad and toss well to coat. Sprinkle with crumbled feta cheese and serve.