Thanks to Jill T for sending this recipe our way. Inspired by a recipe from Eating Well. From Jill: "Made this green soup tonight as soon as I got my bag home. Threw in the beet tops, kohlrabi and broccoli leaves, and half the mustard greens. Really versatile and tasted good. Just in case others are looking for ways to use up greens and creative ways to use leaves/tops."
Heat 1 tablespoon oil in a large skillet over medium-low heat. Add onions and 1/4 teaspoon salt; cook, stirring frequently, until the onions begin to brown, about 5 minutes. Reduce the heat to low, add a splash of water (a few tablespoons) and cover. Cook, stirring frequently and covering the pan, until the onions are greatly reduced and have a deep caramel color, 25 to 30 minutes.
Meanwhile, heat up the stock in another pot. Once it's boiling, add in the rice if using and the remaining salt. Reduce heat to maintain a simmer, cover and cook for 15 minutes. If using beans, heat them up in the stock as well, but only for 5 minutes or so.
Trim the hard center ribs out the greens and coarsely chop.
When the rice or beans have cooked, pour contents of stock pot into the caramelized onions and add the greens. Return to a simmer; cover and cook for 10-15 minutes. Remove from heat once the greens are tender but still bright green.
Puree the soup in the pot with an immersion blender until perfectly smooth or in a Vitamix in batches (return it to the pot). Squeeze in the lemon juice. Taste and adjust seasoning.
** Next time we make this, we're going to try roasting two heads of garlic (cut off the tip of the bulb, splash on some olive oil, and wrap in foil) and 4 lemon halves at 375 for 25-30 minutes or so. Squeeze out the roasted garlic and the juice from the lemons into the soup before puréeing.