Should You Fill Thumbprint Cookies Before Or After Baking?
It is best to fill thumbprint cookies after baking. The indentation made in the cookie dough before baking will expand during the baking process, so filling the cookies before baking may cause the filling to overflow or become caramelized and burnt. Once the cookies have cooled slightly, use a small spoon or piping bag to fill the indentations with jam, chocolate, frosting, or any desired filling.