The puff pastry is the crust...so just roll it out in a baking sheet and pile the ingredients on top. You can fold the edges of the pastry over on top of the potatoes if you have enough to reach. It turns out that Nick has parsnips just lying around in the fridge. I was surprised too. Don't worry, they are not necessary for the recipe to work out. In addition, any starchy root vegetable can be used.

I agree about the Cod. We have such great photos and we made the best food ever. I will start scrounging for recipes that I used. This could be a fun holiday project.