4 tablespoons unsalted butter
1 medium sweet onion, such as vidalia, halved and sliced
2 tablespoons unbleached all-purpose flour
1/4 teaspoon cayenne pepper
1/2 teaspoon ground turmeric
3 cups fresh corn kernels, plus milk scraped from cobs
2 cups low-sodium chicken or vegetable broth
1. In a large saucepan, melt butter over medium heat. Add onion and 1 teaspoon salt; cook, stirring occasionally, until softened, 5 to 7 minutes.
2. Add flour, cayenne, and turmeric; cook 1 minute more. Add corn kernels and milk, broth, and 2 cups water.
3. Bring to a boil, then reduce heat to medium-low and simmer until corn is tender, 8 to 10 minutes.
4. Remove from heat; let cool slightly.
5. Transfer mixture to a blender, working in batches if necessary, and purée until very smooth, 2 to 3 minutes.
6. Refrigerate until cold, at least 4 hours or, in an airtight container, up to 3 days. Season with salt; serve.