Makes about 2 dozen jumbo rings
1 very large onion, peeled, cut crosswise into 1-inch slices, separated into rings, paper-thin skin removed from rings
1 cup all-purpose flour
1 cup pancake mix
1/2 teaspoon salt
1 cup water, plus extra for thinning batter
4 cups plain bread crumbs
1/4 cup sesame seeds
6 cups peanut oil or vegetable oil
Place onion rings in a bowl of water. Measure flour into a bowl. In a separate bowl, combine pancake mix and salt. Mix in 1 cup of water to form a smooth batter. In a third bowl, mix bread crumbs and sesame seeds.
Remove an onion ring from water. Coat in flour, knocking on side of bowl to remove excess flour. Coat in pancake batter, allowing excess batter to drip off , then transfer ring to bread crumbs. Add additional water to the batter as it thickens.
Make a well in bread crumbs, drop in batter-coated onion ring, bury with crumbs, then press crumbs onto the onion ring. Continue with remaining onion rings, stacking in alternating layers in a large, shallow container so the edges touch as little as possible. Refrigerate until ready to use. (Onion rings can be refrigerated, uncovered, up to 24 hours ahead.)
Heat oven to 200 degrees. In a soup kettle, heat oil to 350 degrees. Set a rack over a baking sheet. Drop rings one at a time into oil, fitting in four or five per batch. Cook for 2 minutes, or until rings are a rich brown, turning halfway through cooking. Transfer to rack, sprinkle with salt and serve. (Can be held in a 200-degree oven up to 30 minutes.)