Onion Rings

1 1/2 teaspoons salt
1 3/4 cups flour
1 quart cooking oil
1/2 cup cornmeal
1/2 cup mayonnaise
1/2 teaspoon black pepper
2 cups buttermilk
2 tablespoons cream-style horseradish sauce
2 tablespoons ketchup
3 large onions Spanish or other large onions
onion rings peel the onions and cut them across the equator into 1/2-inch-thick slices separate slices into rings in a large bowl stir together the buttermilk 1 teaspoon of the salt and 1/4 teaspoon of the pepper add onions to buttermilk mixture and toss to coat let sit for 15 minutes meanwhile stir together the flour cornmeal remaining 1/2 teaspoon salt and 1/4 teaspoon pepper in a large bowl place oil in a large dutch oven or stockpot and heat to 350 degrees working in batches and using tongs remove onions from the buttermilk mixture letting any excess batter drip off then coat thoroughly in the flour mixture fry for 2 to 3 minutes turning once halfway through or until golden brown repeat with remaining onion rings checking between batches to allow temperature to come back up to 350 degrees
sauce stir together mayonnaise ketchup and horseradish sauce serve with onion rings