Sourdough Onion Rings

Using a sharp knife, carefully slice the onions into ½" slices. Pull the rings apart.
In a shallow bowl or baking dish, whisk together the garlic powder, flour, black pepper, and salt. To a second bowl, mix together the sourdough discard and seltzer water. To a third bowl, add the panko crumbs.
Toss an onion ring slice into the flour mixture until it's fully coated.
Using a fork, dip the onion ring slice into the sourdough discard batter until fully coated.
Then, toss the onion ring slice into the panko bread crumbs. I like to use my fingers to gently press the crumbs onto the onion ring. Add the battered onion ring to a parchment paper-lined baking sheet. Repeat with remaining onion rings.
While the coated onion rings are resting, heat up the vegetable oil in a large pot or Dutch oven until the thermometer reaches 350°F (176°C).
Using a spider strainer, carefully add two to three onion rings to the hot oil making sure not to overcrowd the pot. Fry for about 2-3 minutes or until the onion rings are golden brown. You will need to fry the onion rings in batches.
Using the spider strainer, remove the onions form the pot and place on a paper towel-lined plate. Repeat with remaining onion rings.
Add the sauce ingredients to a bowl, whisk together, and enjoy!