Power Green Soup

In a 5- to 6-quart pot, heat oil over medium heat. Add onion and celery. Cook until soft and translucent, about 8 minutes. Add ginger, horseradish and garlic; cook 1 minute. Gradually add mustard greens, collard greens and kale. Cook until very soft and wilted, about 5 minutes. Add stock.

Increase heat to medium-high and bring mixture just to a boil. Reduce heat and simmer, uncovered, until everything is very soft, about 20 minutes. Stir spinach into soup until wilted. Working in batches, puree soup in a high-powered blender until very smooth. Season to taste with salt and pepper. Serve with lemon wedges for squeezing over each bowl, if desired.