Blitz the biscuits and butter in a food processor until clumpy and then press the mixture into the bottom of a greased 20cm deep loose bottom cheesecake / cake tin.
Put the biscuit base in the fridge for at least an hour for it to set completely.
To Make The Toffee Sauce
Put the light brown soft sugar and butter into a small saucepan and heat, gently, stirring well with a wooden spoon until thick. Add the light condensed milk and stir again constantly for about 8 minutes until thick and the colour is light caramel.
Remove from the heat and stir in the 4 tbsp. of quark. Set aside and allow to cool for a few minutes.
Pour the toffee sauce onto the set biscuit base and put back into the fridge again for at least an hour for it to set completely.
To Make The Topping
Mix the coffee granules, caster sugar, yogurt and remaining quark in a bowl.
With a hand whisk or preferably in a stand mixer bowl, whisk the double cream until stiff, then gently fold in the yogurt mixture.
Chop both of the bananas into thin slices and scatter the slices from one banana over the set toffee sauce.
In a small bowl add the other banana slices to the lemon juice and keep in the fridge until you are ready to serve the cheesecake.
Spoon the cream mixture onto the banana and toffee mixture.
Put the cheesecake back in the fridge for at least 6 hours (recommended overnight).
When ready to serve carefully remove the cheesecake from the cake tin and decorate with the remaining sliced bananas and dust with the cocoa powder.
Notes
For best result make the night before you want to serve it and refrigerate overnight.*If you cannot get quark cream cheese use any no fat/low fat cream cheese.