The phrase "thin layer of batter" refers to a thin coating of a mixture made from flour, eggs, and other ingredients spread over food before cooking. Full definition
I'd never heard of Baumkuchen — a traditional German cake baked in layers on a rotating spit in front of a grill, whose final spiraling layers resemble the cross-sectional growth rings of a tree [see how it's done]-- but when I got to the Shichttorte — a layer cake made by baking very thin layers of batter one by one on top each other — I realized that I had in fact bookmarked a similar recipe in a cookbook, probably close to fifteen years ago! (korenainthekitchen.com)
Basically you are trying to create an even and thin layer of batter as quickly as possible so that the crêpe ends up thin and delicate and shaped like a circle. (allysonkramer.com)
This is going to be a pretty thin layer of batter but it'll cover evenly just use a small offset spatula and that finesse you got. (witandvinegar.com)