1. Coat your hands with powdered sugar. Press the cake-shaping clay into a layer along the bottom of a cake pan and lightly coat the top of the layer with powdered sugar to reduce sticking.
2. Form a shape into the clay. You can freely form a shape, or can press an object (e.g., a hand) into the clay. If you do not want clay to touch the object, place a piece of plastic wrap over the layer, firmly press the object into the clay, and remove the plastic wrap. This may require slightly more force than if the object is directly contacting the clay.
3. Lightly spray the pan and the clay with cooking spray. Pour cake batter over the clay and bake until the cake is done.
4. Using a knife, loosen the cake (but not the clay) from the edges of the pan. Place a large cookie sheet over the top of the pan, and invert the cookie sheet and pan such that the cake is removed from the pan.
5. Let the clay in the pan completely cool. Cut it into large chunks and remove it from the pan.