Mix the flour with a pinch of mixed spice and salt in a bowl. Beat in the egg yolk, melted butter and sparkling water to make a smooth batter.
Whisk the egg white in a clean, dry bowl until stiff peaks form, then gently fold into the batter.
Heat 2.5 cm (1 inch) of vegetable oil in a deep heavy-based saucepan or deep-fat fryer until hot – 180°C (350°C), or until a cube of bread dropped into the oil browns in 30 seconds.
Peel and thickly slice the banana, meanwhile, then stone and slice the peach, and core and thickly slice the apple.
Dip the slices of fruit into the batter and deep-fry for 1–2 minutes, in batches, until crisp and golden. Drain on kitchen paper.
Dust the fritters with a little icing sugar and serve piping hot with ice cream.