I started with a bakery made cake (I just don’t have the patience for baking and I can never get a good flat sheet cake like the bakery can… And, they can pipe messages on it WAY better than I can). This is a quarter sheet cake.
I made Sonic entirely out of fondant. I used the pre-made Wilton fondant in pure white. I tinted the fondant with regular food coloring. It took quite a bit of sculpting but it was worth it in the end. My son was thrilled with this homemade Sonic cake!