Pour hot water over the small cubes of feta cheese and leave it to drain away its salt for 4 hours, then strain it. Grind the biscuits and add the melted butter to them, stir well and press the mixture to the bottom of the form.
In a bowl, mix the feta with the eggs, sugar, dissolved coffee, sour cream and half the melted chocolate, stir and pour it over the cake layer. Spray the rest of the melted chocolate on top of the mixture and smear with a skewer to create a marble effect.
Bake the cake in a preheated 356°F (180 °C) oven for 40-50 min. Serve the cheesecake cooled and decorated with the caramel.
To make the caramel: Melt the sugar in a water bath, without stirring, until you get a light caramel. Add the butter, stir and pour in the cooking cream, stir until the mixture becomes homogeneous and leave to cool.