Step 2: Make dog-flour
Grind up your kibbles. The amount will differ depending on the size of your cake, aim for about 1/3 of the final cake-volume.
Here I used a magic bullet. But, any blender will work. If you don't have a blender, try a mortar and pestle, or use something heavy to smash them into powder. Get them as fine as you can - we are trying to mimic wheat flour.