For the ice box coffee biscuits, place the butter and sugar into a bowl and beat until light and fluffy, then add the eggs and beat well.
Add the cold coffee and coffee essence and mix well. Fold in the flour, cocoa, bicarbonate of soda and salt and bring together to form a firm dough.
Press into a 2cm/¾in thick block, then wrap in cling film and place in the fridge for one hour to rest.
Preheat the oven to 180C/350F/Gas 4.
Roll the dough out to 5mm/¼in thick, then stamp out into discs using a 7cm/2¾in diameter plain biscuit cutter.
Place onto a baking tray and bake for 8-10 minutes, or until just risen and firm to touch.
For the cake, whisk the double cream with the coffee essence in a bowl until it just holds soft peaks when the whisk is removed from the bowl, then fold in the stem ginger syrup and coffee essence.
Take a large plate or cake stand and place a little cream on the base, then place a 25cm/9in round cake board on top.
Dollop two spoonfuls of cream in the middle and spread out to within 2cm/¾in of the edge, then place one biscuit in the centre and six around it in a circle. Spread a layer of cream over the top, making sure the biscuits are still visible at the side.
Repeat the process layering up the biscuits like bricks, until you have used up all the cream and all the biscuits, finishing with a layer of cream.
Place in the fridge overnight but preferably for 24 hours so that the biscuits soften.
Decorate the top of the cake with the slices of stem ginger. Serve cut into slices straight from the fridge.