For the cookie crust crumb
1. Grind thehomemade OR packet cookies to a powder,then mix in enough melted butter until the cookie crumbs hold their shape when pressed together.
2. Press the crumb mixture evenly and firmly across the base and halfway up the sides of a deep 23cm in diameter springform cake tin on a lipped baking tray.
3. Bake at 180C/140C in fan-forced oven for 20 minutes to cook the crumb,then remove from the oven.
4. Cool slightly and use a straight-sided coffee mug to press the hot crumb mix back up the sides of the tin if it has dropped down.
For the cheesecake
1. Put the mascarpone and castor sugar in a saucepan. Bring the mixture to a simmer and stir until it forms a syrup. Remove from the heat when it boils,then leave to cool.
2. Beat the cream cheese until soft and smooth,then beat in the mascarpone syrup and egg yolks. Next,beat in the sour cream and lemon juice.
3. In a very clean bowl,whisk the eggs whites with the salt to stiff peaks. Fold this through the cheese mixture evenly.
4. Pour the mixture in the springform tin right to the top,and bake at 140C/120C fan-forced for about 75 to 90 minutes,or until the temperature deep in the middle reaches 65C,or just before the middle of the cake fully rises while it's still wobbly.
5. Leave to cool,then chill before serving.
Tip:Freeze the biscuits before crumbing so they grind finely.
For the crust,try mychocolate ginger snap cookie recipe.