Pour enough oil in a medium saucepan to reach a depth of 4-cm. Heat the oil over medium heat until a deep-fry thermometer registers 190°C.
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 1/4 cm slices and separate into rings. Slice each apple into 5 rings and pat dry with kitchen paper.
Dip the apple slices into the batter and allow any excess 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 salted cinnamon sugar. Serve immediately.
For the salted cinnamon sugar:
Mix ingredients together in a bowl and set aside.