Preheat oven to 325. Prepare cake tin. Lightly grease and line the bottom and sides of a round 12 inch spring form tin with greaseproof baking paper or parchment paper). Wrap two layers of foil around the tin to prevent water seeping in. Find a large baking dish that will fit the spring form tin. Fill the empty baking dish 1/4 of the way full with water and place the baking dish with water (don't put the lined spring form tin in just yet) in the centre rack of an oven.
Melt cream cheese, butter and milk over a double boiler, use whisk to get out any lumps. Cool the mixture over an ice bath.
Fold in the flour, corn flour, egg yolks, lemon juice and mix well.
Whisk egg whites with cream of tartar until foamy. Add in the sugar and whisk until soft peaks form and there is no liquid egg white at the bottom. Add one third of the egg white mixture to the cheese mixture to loosen. Then add the rest in third batches and mix well and ensure that the egg whites are thoroughly combined gently by folding - there should be no streaks at all. Divide the batter evenly in two. In one bowl, sift the cocoa in it and combine well using a folding action. The most important thing is that the two batters must be of the same consistency for this cake to work.
Take your lined spring form tin and place tablespoons of cream colored batter in a circle in the center of the tin. Then take 3 tablespoons of the chocolate batter and place in the center. Keep adding circles and the batter will spread of its own accord. After all of the batter is added. Ready to bake in the oven in a water bath. It is very important that you don't tilt the tin, the batter will just spread by itself if they're of the same consistency. Keep adding 3 tablespoon circles of batter until both of the batters are used. If you don't divide them evenly and have batter of just one color leftover, just stopped adding it and bake the leftover separately as not to ruin the zebra effect. Carefully transfer the cheesecake into the water bath in the oven making sure not to tilt the cheesecake. Bake cheesecake in the water bath for 1 hour or until a skewer inserted in the center comes out clean and the top is golden brown. Chill thoroughly.