1 medium yellow-flesh potato, peeled and cut in 1/2-inch cubes
4 cups cold water
1/2-3/4 cup evaporated milk, preferably low-fat
Pinch of cayenne pepper
Salt and freshly ground black pepper
1 tsp. sugar (optional)
1/4 cup chopped scallion, green part only
12-16 medium shrimp, cooked and shelled (optional)
On a chopping board, cut off the corn kernels from each cob and transfer to a medium Dutch oven or deep saucepan. Scrape cobs with the back of the knife to extract milk and remaining corn bits, and add to the pot. Add the scraped cobs to the pot. Add the onion, potatoes and water and bring to a boil. Reduce heat, cover and boil gently until vegetables are tender, about 15 minutes. Remove cobs and discard. Strain soup into bowl, reserving cooked vegetables; there should be about 4 cups of broth. Take out 1/2 cup of the vegetables and reserve.
In a blender, purée remaining vegetables with 2 cups of broth (about half) until mixture is creamy and smooth. Return purée to the pot. Mix in 1/2 to 3/4 cup evaporated milk, depending on thickness of purée. Reheat until hot. Season to taste with cayenne, salt and pepper. If the sweet taste of fresh corn seems weak, add up to 1 teaspoon sugar, if desired.
Divide chowder among 4 bowls. Garnish each with reserved corn and scallions. If desired, garnish soup with cooked, shelled shrimp. Serve. Refrigerate or freeze remaining corn broth to use in making vegetable soup.