Shallow bowl of 2 cups milk whisked with 1 large egg
Shallow bowl of 1 cup flour mixed with 1 cup cornstarch and 1 teaspoon salt
deep fryer or heavy-bottomed pot filled with 4 inches of vegetable oil heated to 365 degrees
Soak the onion rings in the milk mixture for 30 minutes. Toss each ring in the flour mixture; repeat, dipping rings in milk and flour again. Fry in the hot oil until golden, about 5 minutes. Transfer to paper towels; season with salt.