A few years back I had a summer when I ate variations of this soup all of the time. Sometimes I would throw different herbs into the pot. I would also liberally substitute radish or beet greens for mustard, or chard for spinach, etc. Serves 8.
2 lbs. spinach
1 bunch mizuna (about 1/2 lb.)
1 cup loosely packed cilantro
5 cups water
1 tsp salt, plus more to taste
1 large potato, peeled and chopped in large pieces
1 TB, + 1 tsp olive or sunflower oil
2 onions, chopped
1 TB sherry or Madiera, optional
2-3 cloves garlic, finely chopped
4 cups vegetable or chicken broth
1/2 tsp crushed red pepper flakes
1 TB lemon juice
freshly ground black pepper
Wash and roughly chop the greens. Place greens, cilantro, water, salt and potato in a large pot over medium-high heat. Bring to a boil, cover, reduce heat and simmer for about 30 minutes. While greens are simmering, heat 1 tablespoon of the oil in a large heavy-bottomed skillet over medium heat. Add onions and a sprinkling of of salt. Cook, stirring occasionally until onions are golden brown and soft, up to 45 minutes or more. When nicely browned, add liqueur or a bit of water and stir to bring up any remaining bits in the bottom of the pan. Add cooked onions to the pot with greens. Back in the skillet, heat remaining 1 tsp of oil and garlic. Saute for a minute or two until soft. Add to the pot. Add broth and red pepper flakes and simmer for another 10 minutes. Working in batches puree soup in a blender, or use an immersion blender in the pot. Process just until smooth, but do not over blend or the potato can make the soup gummy.
Back in the pot, return soup to a simmer. Add pepper, a dash more salt and lemon juice. Taste and adjust seasonings. Serve garnished with yogurt, feta or goat cheese.