Preheat the oven to 350°F. Separate the filling from the Oreo cookies and crush the cookies.
Mix the cookie crumbs with the other chocolate cake ingredients, divide the batter between two springform pans, transfer both pans to the oven, and bake for 45 minutes. Once the cakes have cooled completely, cut the top to be level and set aside the discarded cake for later. Once level, cut each cake into two layers.
To make the frosting, heat up the heavy cream and melt in the white chocolate. Stir everything together for about 2 minutes to make sure the chocolate has melted completely before adding the Oreo filling. Mix everything together and set aside to cool.
Cut two of the cake layers into 3 rings using two different sized bowls. Cut the other two cakes into 4 rings with the size-specific bowls. If you don't have bowls that fit the specified dimensions, any similar-sized circular object will also work.
Briefly whip the frosting once more before spreading it over the cooled cake. Lay the outer ring of the 3-ring cake on a plate and spread frosting along the inner ring. Lay the second-smallest ring of the cake in the larger ring, spread frosting on the inside, and fill with the smallest piece of the cake. Spread frosting on top of the reassembled layer. Now repeat with one of the 4-ring cakes on top of the reassembled layer. Repeat until all layers are assembled, then spread frosting over the completed cake.
Take the discarded cake from Step #2 and crumble it over the top of the cake. Garnish with whipped cream dollops and more Oreos.
