- 1 cup millet grits or 1 cup whole millet
- 2 tablespoons (¼ stick) unsalted butter or olive oil
- 1 cup chopped leeks (white and light green parts) or onion
- 1 teaspoon dried tarragon
- 1½ quarts low-sodium chicken or vegetable broth
- 1 package (10 ounces) mixed frozen carrots, corn, and peas (sometimes called classic mix)
- 1 to 1½ cups well-shaken buttermilk, plus a bit more for serving
- Salt and freshly ground black pepper
- If using whole millet, grind it to grits in three or four batches in a spice grinder. It’s okay if the grits vary in size.
- Set a heavy 6-quart soup pot over medium heat. Add the millet and toast, stirring frequently, until the millet emits a distinct cornlike aroma, about 3 minutes. Transfer the millet to a bowl.
- Add the butter to the soup pot, and as it melts, stir in the leeks. Cook until the leeks begin to wilt, about 4 minutes. Stir in the tarragon and cook for another minute.
- Add the broth and millet and bring the soup to a boil over high heat, stirring constantly to prevent the grains from sinking to the bottom. If lumps develop, squash them against the side of the pot. Cover and simmer over medium-low heat, stirring frequently, until the millet is just about tender, 10 to 12 minutes.
- Stir in the frozen vegetables. Cover and continue cooking until the vegetables and millet are tender, 3 to 5 minutes. Stir in enough buttermilk to give the broth the creaminess of a pureed split-pea soup. Season well with salt and pepper.
- Ladle into bowls. Drizzle a little buttermilk in a swirl on the top of each portion.