Pour enough oil in a medium saucepan to reach a depth of 2 inches. Heat the oil over medium heat until a deep-fry thermometer registers 375 degrees F.
In a medium mixing bowl whisk the egg white until frothy. Stir in the beer. Add the flour and salt. Mix until the batter is smooth. Set aside.
Cut the onion into 1/2-inch slices and separate into rings. Slice each apple into 5 rings and pat dry with paper towels.
Dip the apples slices into the batter and allow any excess batter to drip off. Fry for 1 to 2 minutes each side until golden brown. Using a slotted spoon, transfer the fried apple rings to paper towels to drain. Repeat with the onion rings.
Transfer the apple and onion rings to serving platters. Sprinkle the onion rings with salt. Sprinkle the apple rings with the Salted Cinnamon Sugar. Serve immediately.
Salted Cinnamon Sugar:
Combine all ingredients in a small bowl. Store airtight in a glass or plastic container.