Peel the potatoes and cut them into medium pieces. Place them in a saucepan of cold, salted water. Bring to the boil and simmer until soft enough to mash.
Heat the oven to 180°C.
Grease a shallow pie dish, roughly 24cm wide. Lay the pastry over the top and gently press it into the bottom edges. Let the excess hang over the edge.
Use fork prongs to make lots of holes in the bottom of the pastry.
Bake in the oven for 15 minutes (press the pastry bottom down if it rises up).
Take it out of the oven and use a sharp knife to carefully cut off the pastry overhang.
Heat a drizzle of oil in a frying pan. Add the leeks and fry on a medium heat for 5 minutes, breaking them up a little with the back of a wooden spoon as they fry.
Mash the potato until smooth. Stir in the soft cheese, rosemary and leeks and season with salt and pepper. Stir until combined.
Spoon the mixture into the pastry case. Spread evenly.
Press the camembert wedges into the mixture at equal intervals.
Cover with grated cheese.
Bake in the oven for 25-30 minutes.
