Cheese and Potato Pithivier with Sharp Green Salad

You’ll need to start this the day before you wish to serve it, as the pastry needs several stages of chilling and dauphinoise requires overnight chilling.

Pastry

1. In a large bowl mix together the flour, salt and cold grated butter.
2. Pour in the water and mix briefly to form a dough.
3. Tip it out onto a large sheet of baking paper, then briefly roll it vertically so it's a bit bigger than an A4 sheet of paper. 
4. Using the paper to assist you, fold the top third down and the bottom third up and over that. Wrap in cling film or baking paper and refrigerate for 2 hours or until it is firm and no longer slightly sticky to touch. 
5. Lightly dust the work surface with flour. Take the pastry out of the fridge, making sure the open seam is lined up vertically and the top and bottom are open folds. 
6. Roll the pastry out length ways and vertically to the size of approx. two sheets of A4 paper joined together (about 60cm/23½ in total length). 
7. Make a double fold by folding the top quarter down to the centre and the bottom quarter up to the centre before folding these two pieces together to close it like you would a book, then turn this so that the seam is again lined up vertically. 
8. Wrap in clingfilm or baking paper and refrigerate for a minimum of 2 hours or until firm. 
9. Repeat this step. 
10. Once rested, the pastry is then ready to use (keep it chilled until you are ready to use it). 

Dauphinoise 

1. Peel the potatoes, then wash and dry them.  
2. Use a mandolin or a sharp knife and thinly slice the potatoes (to about 2mm thickness), trying to do this lengthways or a way that means you get as much surface area as possible, as this will help in the layering process. 
3. Once sliced, do not wash them as you need the starch to help bind them. 
4. In a large pan, add the cream, milk, the garlic, salt, black pepper,  rosemary and thyme and warm over a low heat until gently steaming – keep an eye on it and stir from the bottom frequently to prevent it catching. 
5. Add the sliced potatoes to the warm cream and milk mixture. Stir well and keep this going over a low-medium heat for approx. 7-10 minutes until the potatoes are slightly tender, not cooked but softened and coated in the cream mixture - it should all be bubbling gently. 
6. Meanwhile, preheat the oven to 180°C fan/200°C/gas mark 6. 
7. Take two large pieces of baking paper and roughly press them into the casserole dish - the paper will help you to remove the baked potatoes later, so bear this in mind. 
8. Using a slotted spoon, layer up the potatoes in the lined casserole dish - this doesn't need to be really precise, but it will help to get a good slice through later if the potatoes are layered nicely. Keep the rosemary and thyme stems out of the casserole dish and discard. 
9. After each layer, ladle in some of the warm cream mixture.
10. Repeat until you have used up all the potatoes, then pour any remaining liquid over the potatoes. Put a lid on or cover with foil and bake for 45 minutes. 
11. Reduce the oven temperature to 160°C fan/180°C/gas mark 4, then remove the lid/foil and bake for a further 20 minutes. 
12. The dauphinoise is ready when you insert a knife and it doesn't meet too much resistance and it feels soft but not mushy. Remove from the oven and allow to cool fully before covering with clingfilm and refrigerating overnight. 

Pie assembly

1. To assemble the pie, line the sturdy baking tray with baking paper (it's important to use a rimmed baking tray as some of the butter will spread onto the tray as the pie bakes).
2. Divide the pastry into two pieces, making one piece slightly larger than the other.
3. Roll out the smaller piece to a 35cm (14in) square, and the larger piece to a 40cm (16in) square, then place the smaller square on the lined baking tray. 
4. Remove the baked potato dauphinoise from the fridge and carefully flip the potatoes onto the pastry round, placing them in the middle. The potatoes will have set into one piece, so they will be really easy to work with. The diameter of the potatoes will be approx. 25cm (I0in), which will leave a border around the edges when pieced in the middle. 
5. Top the potatoes with the cheese slices. Take the second (larger) square of pastry and lay this over the potatoes. Use your hands and fingertips to press and shape the pastry over the potatoes, pressing the pastry edges together to seal. 
6. Trim around the pastry edges using a sharp knife in a circle following the dauphinoise shape, leaving a 2.5cm (1in) border all around.
7. Use your fingers to create a pinched scallop effect around the edge of the pie before baking. 
8. Beat the egg and the remaining 2 tablespoons of milk together for the egg wash, then brush this all over the pie. Use the tip of a sharp knife to make a small hole in the top of the pie. 
9. Chill in the fridge for 30 minutes. 
10. Preheat the oven to 200°Cfan/2200C/gas mark7. 
11. Bake for 30 minutes, then reduce the oven temperature to 180°C fan/200°C/ gas mark 6 and bake for a further 30 minutes until golden all over. The base should also be golden rather than pale -you can check this by gently lifting up one edge, if it's not quite ready, return to the oven for a little longer. 
12. Remove from the oven and allow to cool for 20 minutes before serving in slices. This pie is brilliant served warm with a sharp salad but is also great cold.

Green Salad

1. Stir all ingredients in a small bowl with a small whisk or a fork until the ingredients are completely mixed together.
2. Taste, and adjust as necessary. If the mixture is too acidic, thin it out with a bit more olive oil.
3. Pour over/toss the salad leaves in the dressing. 
4. Slice pickled walnut and serve alongside.