We found this recipe at the Smoke Stack and Jack Stack chain restaurants while researching a story on Kansas City barbecue. Locals told us these onion rings were the best, and after you try them, we think you'll agree.
4 large yellow onions, peeled
4 1⁄4 cups flour
1 cup cornmeal
3⁄4 cup cornstarch
1⁄3 cup baking powder
2 tbsp. dried parsley
2 tbsp. seasoned salt, such as Lawry's
1 cup milk
1 cup buttermilk
1. Cut onions crosswise into 1"-thick slices and separate into rings. Place rings in a large bowl of cold water and soak for at least 30 minutes to remove any bitterness.
2. To make dry batter, mix together 2 1⁄4 cups of the flour, cornmeal, cornstarch, baking powder, parsley, and seasoned salt in a large bowl, then cover and set aside.
3. Pour enough oil into a cast-iron pot to come to a depth of 3". Heat over medium-high heat to 325°–350°. Put remaining 2 cups flour in a bowl. In another bowl, mix together milk and buttermilk.
4. Drain onions. Working in batches, about 3–5 rings at a time, dredge onions in flour, then dip in milk mixture, then dredge in dry batter. Immediately fry onions in hot oil until crisp and golden, about 2 minutes. Use tongs or a slotted spoon to remove onion rings from oil; drain well on paper towels before serving.