- Heat butter or oil in a large, heavy skillet over medium heat, and cook green onions and celery for 2 to 3 minutes, until just tender.
- Hold one corn cob over a bowl and, using a very sharp knife, cut kernels off; reserve cob. Repeat with remaining corn. Holding cobs over bowl, scrape each with the flat edge of a butter knife to extract the milk. Add all of the corn kernels and the corn milk in the bowl to the cooking pot. Add corn cobs to pot.
- Add squash, 1/2 cup water and thyme sprigs to the pot. Cover and simmer for 15 minutes. Remove and discard cobs and thyme sprigs.
- Transfer to a food processor and purée until soup is mostly smooth, but still has some texture. Add milk; season to taste with salt and pepper.
- To serve, divide soup among four individual bowls. Sprinkle tops with finely chopped fresh thyme, and serve hot.
• Skip the thyme and add 1/2 small chipotle pepper to the soup just before puréeing; garnish with avocado slices and a dollop of sour cream.
• Leave out the thyme and add 1 small avocado and 1/2 cup chopped cilantro before puréeing.