Heat vegetable oil in a deep-fryer or pot to 365℉. Onion slices should be about ¼ inch thick. Separate the onion slices into rings and set aside.
In a bowl, combine flour, baking powder and salt.
Dip the onion slices in the flour mixture until completely coated and set aside.
Whisk the eggs and milk into the flour mixture.
Dip the floured rings into the batter to coat and place on a wire rack to let excess batter drip off.
Pour the bread crumbs in a large bowl. Gently toss battered onions into the bread crumbs and and coat evenly.
Deep fry a few rings at a time for 2-3 minutes, or until golden brown.
Place finished onion rings on paper towels to drain.
Season with seasoning salt and serve.
Notes
Tone down onion-flavor: Sometimes, the onion odor can be overpowering. Soak onion slices in buttermilk for 5 to 10 minutes before dredging them in batter. Don't have buttermilk? Make your own. For every one cup of milk, add 1 tablespoon of lemon juice or vinegar. Stir together, and it's ready to go.
Pancake mix onion ring batter: Substituting pancake mix in place of all-purpose flour is also a possible alternative.
Homemade fry sauce: When we go to local restaurants, our favorite dipping sauce is fry sauce (Utah thing). You can find our homemade fry sauce recipe here.