I made these for my two-year-old niece who loves the Cars Movies. Her favorite characters are Lightning McQueen and Mader, of course, but she also likes Flo so I added this one to the group.
This was the first time I had encountered Butter Bleed with my royal icing. The outside edges of the white royal icing in the background turned a light yellow. It looked a bit like a yellow ring.
I'm not completely sure what contributed to this. I had flooded these cookies a few days before and let them sit before I added the cars. I also think the cookie dough may have had a bit more butter as proportionate to flour than it usually does. I also used my oven trick to prevent craters as I described here. I think putting the white dried royal icing base into the oven (even at a very low temperature) was the main problem. I think it heated up the cookie just enough to cause the butter in the cookie to seep into the royal icing. In the future, I will only use this trick to quickly set icing that is still wet. I think a fan or dehydrator might have served me better with this project.