I recently had this pie at Calum Franklin's London restaurant, The Pie Room. It's a rich and wonderful chunk of potato dauphinoise surrounded by cheese and beautifully tasty and shiny pastry. This is my slightly different version - it's a lot of work to make a pie, but absolutely worth it.
Use your favourite strong cheese or a mixture of cheeses. I used some sliced emmental and some grated mature cheddar.