In the bowl of a stand mixer (or using an electric hand mixer), mix the sugar and butter until creamy. Add the eggs one at a time, then the vanilla. Sift together flour, cocoa and salt and add them into the robot. Mix until a smooth paste. Reserve 70g of dough for decoration, wrap it in cling film and put it in the refrigerator.
Divide the remaining dough into 2 balls. Cut a disc baking paper of the size of the tart tins and place at the bottom of each tin and place over a pasta balls. Spread each ball in a tin, smoothing the surface with your fingers. Bake both tins for 25 minutes then let cool 20 minutes before taking the cakes out of the tins.
Prepare vanilla icing
In the bowl of the stand mixer (or using an electric hand mixer), mix the sugar, butter, vanilla and milk until smooth and creamy. Line the round cake tin with baking paper or cling film and fill with the icing using a spatula. Refrigerate 1 hour (or put 20 minutes in the freezer).
Prepare decoration
On a floured board, roll out the remaining dough to 3mm thick. Using a knife, cut 8 1.5cm squares, one 1cm square and one 2cm square. Then cut each square again in 4 by drawing diagonals (you should get small triangles)
Using letter-shaped cookie cutters, cut the word "OREO" and 15 "I". Then form about 25 small balls slightly smaller than a pea. Roll the remaining dough in a thin sausage that will form the oval around the word OREO.
Put all the cuts on a baking tray covered with baking paper and put in the refrigerator. Once the two large cakes are baked, bake the tray for 8 minutes at 180°C and let cool on the tray.
Assemble the giant Oreo
Place one of the cake, facing up, on a serving dish. Top with the disc buttercream filling and cover with the second cake, facing down.
To add the decorative elements, use the chocolate icing pen like a glue and place them like on the picture. Voilà!
Recipe by Anne-Sophie Vidal - Fashion Cooking at https://www.fashioncooking.fr/2016/09/giant-oreo-special-mould/