Leave to chill in the fridge for 30 minutes. For the filling, cook the apple slices in a pan of boiling water for 1-2 minutes, or until just tender but still holding their shape. Drain and cool.
Whisk a little icing sugar and lemon juice into your apple juice to get the right balance of sweetness and acid, remembering that when frozen the power of both sweetness and acidity are diminished.