2 large yellow onions – peeled and sliced into 0.5-inch-thick rings
8 cups water – ice-cold (for soaking)
1.5 cups all-purpose flour
0.25 cups cornstarch
1 tsp baking powder
1.5 tsp kosher salt – divided
0.5 tsp black pepper – finely ground
0.5 tsp paprika
0.25 tsp cayenne pepper
1.25 cups lager beer – cold
48 ounces vegetable oil – for frying
Instructions
Separate the sliced yellow onions into individual rings and submerge them in a bowl of ice-cold water; soak 20 minutes to mellow sharpness and help them stay crisp.
Set a heavy pot or Dutch oven over medium heat and add vegetable oil to a depth of about 2 inches. Heat to 350–365°F, monitoring with a thermometer.
While the oil heats, whisk 1 cup of the all-purpose flour with the cornstarch, baking powder, 1 teaspoon kosher salt, black pepper, paprika, and cayenne in a medium bowl. Whisk in the cold lager beer until smooth and the consistency of thin pancake batter. Let stand 10 minutes.
Drain the onion rings and pat completely dry between kitchen towels. Put the remaining 0.5 cup flour in a shallow dish for dredging.
Working in batches, dredge onion rings lightly in the flour, shaking off excess. Dip each ring into the batter, letting excess drip back into the bowl.
Fry the battered rings in batches without crowding, 2–3 minutes total, turning once, until deep golden and crisp. Maintain the oil at 350–365°F.
Remove to a wire rack set over a baking sheet to drain and immediately season with the reserved salt. Repeat with remaining rings, returning the oil to temperature between batches.