Stem ginger mousse cake

Method

1. Remove and set aside the base from the springform tin, grease the sides of the tin and sit it on a flat serving plate or cakestand, holding it in place with pieces of Blu-Tac on the outside. Line the sides of the tin with non-stick baking paper. 
2. For the base, put the ginger biscuits in a plastic bag and crush with a rolling pin into fine crumbs. Melt the butter in a medium pan over a low heat, then stir in the biscuit crumbs and ground ginger. Spoon the mixture onto the plate/stand inside the tin, then pack it down carefully to make a flat base and chill in the fridge. 
3. For the mousse, put 5 tbsp cold water into a small pan and sprinkle over the gelatine powder. Set aside. Whizz the stem ginger pieces in a mini food processor until finely chopped (or finely chop by hand).
4. Whisk the eggs, egg yolks and both sugars in a large bowl using a hand-held electric mixer for about 8 minutes until the mixture is thick and pale and leaves a trail when drizzled from the beaters. Gradually whisk in the stem ginger syrup. 
5. Gently warm the pan with the gelatine until dissolved and clear, then remove from the heat. Whip the cream in another bowl to soft peaks. Gradually whisk the gelatine into the egg mix using an electric mixer. Rest the base of the bowl in iced water and fold the mix gently with a large spoon until it starts to thicken. Fold in the cream and chopped stem ginger. 
6. Pour the mixture onto the chilled biscuit base and cover with cling film, making sure it doesn’t touch the surface. Chill until set (for at least 6 hours but ideally overnight). 
7. Just before serving, carefully remove the sides of the tin and gently peel off the baking paper. To decorate, whip the cream into soft peaks. Gently spread some over the top of the mousse and draw lines with a palette knife. Spoon the remaining cream into a piping bag fitted with a star nozzle and pipe it around the edge of the cake. Scatter with the crystallised ginger, then decorate with pieces of gold leaf. Serve cut into wedges.