Combine the flour, egg yolk, cider and spice in a medium bowl and whisk until smooth. Set batter aside to rest.
Core the apples, then slice into 3-4mm-thick rings, pat dry with paper towels and dust in the extra flour.
Pour oil into a medium saucepan to a depth of 4-5cm and heat to 165-185°C. (If you don’t have a cooking thermometer, drop a grain of rice into oil and if it comes to the surface quickly and begins to cook, the oil is ready.)
Dip apple rings into batter, let excess run off, then carefully lower into hot oil using metal tongs. Cook in batches of 2-3 slices, for about 1 minute on each side. Once brown all over, remove with tongs and dip into cinnamon sugar.
Serve warm fritters with caramel sauce and vanilla ice cream.