Dauphinoise Pithivier

Instructions

1. Slice the potatoes: Peel the potatoes and slice them as thinly and consistently as possible, about 2-3mm thick. Use a mandoline if you have one, or a sharp knife. Keep them all the same thickness so they cook evenly. Take your time, especially towards the end when the potato gets smaller.
2. Arrange in a large pan: Spread the potato slices in a large frying pan with a wide surface area. A large pan is much better than a deep pot. The potatoes can sit in one or two layers and cook evenly without sticking or breaking.
3. Add the cream mixture: Pour in the double cream, milk, and add the bunch of fresh thyme and crushed garlic cloves. Season generously with salt and pepper. The liquid should just cover the potatoes.
4. Cook the potatoes: Place the pan over low heat and bring to a gentle simmer, don't let it boil rapidly. Put a lid on slightly ajar to let steam escape. Cook for about 15 minutes, giving the pan an occasional gentle shake to ensure even cooking, until the potatoes are knife-tender but still have a tiny bit of bite. They'll finish cooking in the oven.
5. Drain and save the cream: Carefully drain the potatoes through a colander set over a large bowl to catch all that beautifully infused cream. This liquid will be used for the filling! Set the potatoes aside to cool.
6. Prepare the vegetables: Slice the mushrooms. Slice the leek thinly. Wash the leek slices thoroughly in a colander to remove any grit.
7. Caramelise the leeks: Heat a drizzle of olive oil or butter in a large frying pan over medium heat. Add the sliced leeks with a pinch of salt and cook, stirring occasionally, for about 8-10 minutes until they're soft, sweet, and lightly caramelised.
8. Add the mushrooms: Add the sliced mushrooms to the pan with the leeks. Cook for another 5-7 minutes until the mushrooms have released their liquid and everything is cooked down and cohesive.
9. Add garlic: Grate in the 2 garlic cloves and stir for about 30 seconds until fragrant.
10. Make the sauce: Sprinkle the tablespoon of flour over the mushroom mixture and stir well. Gradually pour in the reserved cream and milk from the potatoes (the infused liquid you saved). Stir constantly as it thickens into a rich, creamy sauce. This needs to be very thick, cook it down until it's really thick and holds its shape when hot. This is crucial so it doesn't leak out of the pastry.
11. Add cheese and season: Stir in the 100g grated parmesan. Taste and season with more salt and pepper if needed. Set aside to cool completely.
12. Prepare the pastry: Cut the sheet of puff pastry in half. You'll use one half as the base and one half as the top. Place one piece of pastry on a lined baking tray.
13. Start layering: In the centre of the pastry base, start building a dome shape. Begin with a circle of overlapping potato slices. Season with salt and pepper, then add a spoonful of the mushroom-leek filling. Grate over a little extra parmesan.
14. Continue layering: Keep layering potatoes, filling, and parmesan, building up and inwards to create a dome shape. Take your time and make it look nice, this is your showstopper! Season between each layer. Finish with a final layer of potatoes to create a smooth dome top, with a little more salt, pepper, and cheese.
15. Brush with egg wash: Beat the egg yolks. Brush egg wash around the exposed pastry base (the border around your dome).
16. Cover with pastry: Roll out the second piece of puff pastry slightly so it's large enough to cover your dome. Lay it carefully over the top and press down around the edges to seal, pushing out any air pockets as you go.
17. First chill and glaze: Brush the entire pithivier with egg wash, getting into all the crevices. Place in the fridge for 15-20 minutes until the glaze sets and looks shiny.
18. Second glaze: Remove from the fridge and brush with egg wash again. This double glazing creates a deep, dark, glossy finish. Return to the fridge for another 10 minutes while you preheat the oven to 190°C (170°C fan/ 375°F).
19. Trim the edges: Remove from the fridge. Using a sharp knife, carefully cut around the edge to trim away excess pastry, leaving about 2cm border.
20. Create the scalloped edge: Using a toothpick or skewer, make small indentations all around the trimmed edge, creating a beautiful scalloped pattern.
21. Make a steam hole: Cut a small cross in the very centre top of the dome, cutting all the way through both layers. Use your skewer to gently fold open the points, creating a decorative steam vent.
22. Score the classic pattern: This is the signature pithivier decoration! Using a sharp knife, score curved lines from the centre hole outward toward the edges, creating a scalloped sunburst pattern. The cross divides your pithivier into four sections, score 3-4 curved lines in each section. Score through the egg wash but not all the way through the pastry, you just want to mark it.
23. Bake: Place in the preheated oven and bake for 35-40 minutes until the pastry is deep golden brown and puffed. In the last 10 minutes, you can increase the temperature to 200°C (180°C fan) to get that gorgeous dark colour. The bottom should be crisp and the pastry completely cooked through.
24. Rest and serve: Let the pithivier rest for 5-10 minutes before slicing. Cut into wedges using a sharp knife, making sure to cut all the way through. Serve hot with a simple green salad.