Spring Onion Soup

2 tablespoons extra-virgin olive oil, plus more for drizzling

2 pounds spring onions (or yellow onions), trimmed and thinly sliced

2 1/2 teaspoons coarse salt

1 1/4 cups homemade or low-sodium store-bought chicken stock

2 cups water

8 pieces crisp flatbread, for serving

Heat oil in a large pot over medium-high heat. Add onions, and cook, stirring occasionally, until translucent but not brown, about 15 minutes. Stir in salt, stock, and water. Bring to a simmer, and cook for 15 minutes. Remove from heat, and let cool for 20 minutes. Working in batches, puree in a blender, starting on low speed and gradually increasing to high, blending until soup is smooth. Divide soup among 4 bowls, drizzle with oil, and serve with flatbread on the side.