I used one cake mix. Poured some into a 9 inch round and some into a 6 in round. Once they cooled, I biased sliced the 6 inch in half to have two ears. I did need to trim one to make it flat on top. I then iced the 6 inch cakes with white decorator frosting, crushed Oreos (minus the creme). I found the Oreos stuck better if they were crushed to dust.
I held each 6 inch cake in the air with a waxed paper on the bottom and a bit on the sides and poured on the Oreo dust. A pan underneath caught the excess. As I poured it on I pressed it in with my hand. It took about 40 cookies. I then place my face template on the 9 inch and poured on the Oreo on the edges.
Next, I placed the cakes on a cake board covered with wrapping paper (I put each cake on a cut to size piece of waxed paper). I then lifted the template and gently pushed the Oreos back into place. Next I used a toothpick to draw my face into the base icing. Using a star tip, I did the face starting on the outside. I used Wilton's "copper". Then I did pupils, nose and mouth edges with a star tip . Next whites of eyes and mouth. And finally the black using a piping tip. I wish I had used that tip for the line under the eyes, but it wasn't worth trying to remove it.
At this point I decided to add the eyelashes & bow to turn Mickey in to Minnie. I wasn't sure what to use for the pink bow and had planned to use frosting, but it was getting late and seemed rather impossible to support the middle so I stole a bow from the girls' closet and stuck it on.
The kids were thrilled. They liked the Oreo topping, but I thought it might have tasted better it I hadn't spread the base layer so thin. I really wanted to make her look realistic. It's all about the chin.