Ingredients

Step by step

1. You need to start this recipe a day ahead to allow for chilling time. Sauté the onions with the oil, butter and a pinch of salt until soft and well browned, stirring occasionally (about 30 minutes).
2. Meanwhile, put the cream, milk, rosemary, thyme, garlic and salt into a wide pan (a deep frying pan or saucepan) and warm together on a low heat while you prepare the potatoes, but don’t let it boil.
3. Slice the potatoes on a mandoline (or with a knife) to 2.5-3mm thickness and drop into the cream mixture. Bring to a simmer, stirring constantly, and cook for 3-4 minutes until just tender. The cream will have thickened considerably, due to the starch from the potatoes. Drain into a colander set over a large bowl, keeping the cream mixture. Preheat the oven to 200°C, fan 180°C, gas 6.
4. Line a deep 30cm x 20cm base ovenproof dish with baking paper and lay a third of the potato into the dish. Scatter half the cheese across the surface and pour in a third of the cream mixture. Layer in another third of the potato and then spread all the onions across the surface. Scatter on the remaining cheese and layer the rest of the potato on top. Pour another third of the cream mix all over, then press a sheet of baking paper onto the surface. Bake for 35 minutes.
5. Remove from the oven, remove the paper; add the last of the cream mix. Press the paper back on, reduce oven to 190°C, fan 170°C, gas 5; cook for 20 minutes or until the potato is soft. The dish should be saucy and not dry.
6. Cool the whole dish on a rack to room temperature – at least 2-3 hours. Then chill in the fridge for a couple of hours, preferably overnight, until really firm.
7. Roll out 500g pastry on a floured surface to make a large rectangle 5mm thick. Trim to make a pie base 35cm by 25cm. Transfer to a lined baking tray and chill for 10 minutes in the fridge or freezer. Discard the top paper from the dauphinoise, loosen the paper at the edges of the dish and quickly flip over onto the pastry.
8. Roll out the remaining pastry into a rectangle large enough to cover the potatoes and join with the base pastry. Trim to neaten and crimp the edges together (use pastry trimmings for decoration). Beat the egg yolks with a pinch of salt and brush the whole pie with the glaze. Chill for 10 minutes, or until firm, then glaze again for a really rich colour. Cut a steam hole, then bake at 200°C, fan 180°C, gas 6 for 45 minutes or until golden brown. Rest for 10-15 minutes before slicing.