Preheat the oven to 180°C/350°F/Gas Mark 4.

Bring a pot of water to a boil. Cut the potatoes into thin slices and add them to the water. Cook for 12 minutes.

Cut the leek into thin slices. Crush the garlic. Grate the cheese.

Heat a frying pan over high heat. Once hot, add the bacon and cook until crispy. Remove the bacon from the pan and set aside.

In the same frying pan, add the leek and cook for 6 minutes. Add half the garlic and fry for 1 minute.

Add the crème fraîche, vegetable stock, Parmesan, and 50ml of water. Mix together, bring to a boil, then reduce the heat and simmer for 2 minutes. Take off the heat and stir in the blue cheese until melted.

In an oven-proof dish, layer the potato slices. Pour the sauce over the potatoes. Cover with the puff pastry. Place into the oven and cook for 25 minutes.

When there are 8 minutes left on the pie, add the green beans to the frying pan and fry for 6 minutes. Add the rest of the garlic and fry for another 1 minute.

Cut the pie in half and place on plates. Place the green beans on the side.