To make the base, melt the butter and sugar in a saucepan over a gentle heat and stir in the crushed biscuit.
Press the mixture evenly in to the base of loose-bottomed cake tin. Place in the fridge to chill.
To make the filling, place the cheese in a large mixing bowl. Beat in the egg yolks, half the caster sugar, the lemon zest and juice, the cream and the marmalade.
Put the gelatine and water into a small heatproof bowl over a pan of simmering water and stir until dissolved.
Beat the gelatine mix into the cheese mixture then put to one side.
Whisk the egg whites until stiff, then whisk in the remaining caster sugar. Fold into the cheese mixture then spoon into the prepared tin. Chill for 3 to 4 hours.
Remove the cheesecake from the tin when set. Warm the marmalade, mandarin slices and ginger together in a small pan then carefully tip over the cheesecake and chill again before serving.
For best results allow to chill for 4 hours.