Why did it come out perfectly flat? It didn’t curl up on the sides like your picture. And it didn’t get those billows in the middle.

Hi dmtran, sorry to hear that! My hunch is that the pan wasn't hot enough.

I’ve made a puff pancake only once, but if memory serves, you have to beat the eggs really well to get air into them, and the pan in the oven has to be blistering hot before you pour the batter into it.