Heat the oil over low-medium in a large pot. Once hot, add the onion and cook for about 10 minutes, stirring frequently, until translucent but not too browned. If the onions are browning too much, reduce the heat.
2 teaspoons oil, 1 medium onion
Add the potatoes, broth, salt, and pepper. Cover and increase the heat to bring the soup to a boil, then reduce the heat and simmer, covered, for about 10 minutes or until the potatoes are fork-soft.
400 grams floury potatoes, 750 ml vegetable broth, 1 teaspoon sea salt, ½ teaspoon black pepper
Stir in the sorrel. Use an immersion blender or heat-safe blender to mix until very smooth. Season to taste and serve hot, optionally topped with cream and herbs like chives.
100 grams sorrel
Sorrel soup should be stored in the refrigerator and can be frozen.