Grind the biscuits to fine crumbs and mix them with the softened butter, sugar and cocoa. Spread them out into a layer in the form in which you will be making the cheesecake, applying pressure with your hands. It is best to use a form with removable walls.
For the cream, all the products need to be at room temperature, they must not be cold. Add all of the cream cheese and beat it well with the sour cream and sugar until you get a smooth and homogeneous cream. Add the flour to it, stir and start adding the eggs one at a time, constantly beating.
I used a mixer, but it can be done by hand. Once they are well beaten, you are going to get a fluffy cream. To it, finally add the vanilla and grated lemon rind. Divide the mixture into 2 parts - 2/3 and 1/3 of the whole. Color the smaller part with the pre-melted and slightly cooled chocolate, add 1 tablespoon of cocoa.
Leave the larger part to remain light in color. Pour half the light cream over the layer in the form, sprinkle it with chocolate chips and pour in the chocolate cream, while trying to get waves between the two creams. In order to do this, pour the chocolate cream in suddenly. Smooth the top out with the remaining half of the white cream.
Put the marble cheesecake to bake in a preheated 428°F (220 °C) oven, with the fan on if possible. Bake for 5 minutes at high heat, then reduce to 266°F (130 °C) and bake for another 25 minutes. Turn off the oven but do not remove the cheesecake.
Leave it there until completely cooled - for a couple of hours. The final decoration is entirely up to you - you can use fruits.