This quiche Lorraine is ambiguous: thought to be as French as Edith Piaf, its origin and name (related to the german Kuchen) is German.  Regarded an easy dish, this version is anything but.

It is based on the recipe found in the book ‘Heston Blumenthal at Home’ which makes it by definition challenging to execute. But do not be discouraged, it will be an instant hit at your dinner parties. Plus it can be prepared a day in advance as this helps the custard filling to set properly. For the best flavour, it should be served warm or at room temperature. Serves 6 or hungry 4.

For the pastry

• 230g all purpose flour
• 1/2 tsp sea salt
• 100g cold unsalted butter, cubed
• 25g egg, lightly beaten (approx. 1/2 large egg)
• 40g cold tap water

For the filling

• 40g unsalted butter
• 4 large onions, peeled  and finely sliced
• 200g bacon lardons
• 3 large eggs
• 300g whipping cream
• 80g grated gruyère cheese
• 20g grated parmesan cheese
• sea salt and freshly ground black pepper
• nutmeg

For the pastry put the flour, salt and butter in a mixer fitted with the paddle attachment and combine until the mixture resembles breadcrumbs. Change to the hook attachment and add the cold water and the egg. Continue mixing until dough comes together to form a ball. Shape the dough into a disc, wrap in clingfilm and refrigerate for 30 minutes.

For the filling, melt the butter in a large heavy bottomed pan over medium heat. Add the onions and cook stirring occasionally for 10 minutes until they have softened and are translucent. Reduce the heat to medium-low and cook for about 40-50 more minutes, stirring occasionally, until the onions are soft and golden in colour. Drain the onions from any excess butter when cooked.

Tip the lardons in a small frying pan over low heat and fry them until just cooked, but not coloured. This should take about 5 minutes. Drain off any liquid that comes out and discard. Drain the lardons on paper towel.

Place the pastry between two sheets of baking parchment and roll out to a thickness of 2mm.

Butter a 24cm fluted tart tin, line with the pastry and gently push it into the base and edges,allowing the excess to hang over the sides. Prick all over the base of the tart with a fork and refrigerate for 30 minutes.

Preheat the oven to 170°C.

Cut a large circle of baking parchment and scrunch it  up a couple of times. Lay it over the pastry base, fill with beans or coins and bake for approximately 20 minutes before removing the beans or coins and parchment. Return the pastry case  to the oven and bake for a further 5-10 minutes, until golden brown. Remove the tart tin from the oven ,let cool a little and then, using a sharp knife, cut the excess pastry from around the top of the tart tin.

Reduce the oven temperature to 120ºC.

Combine the cream with the eggs in a saucepan and then add the cooked onions, lardons and the cheeses. Season with salt, freshly ground pepper and a pinch of freshly grated nutmeg. Place the pan over medium heat and bring the mixture to 63ºC, stirring constantly. This will take about 15 minutes.

Make sure the case is still warm when filling, if necessary reheat in the oven.

Fill the case with the cream mixture and return to the oven, until the temperature of the quiche filling reaches 70ºC. This will take approximately 30 minutes.

Allow to cool at room temperature for 20 minutes, then place in the refrigerator, preferably overnight. Then, before serving , bring back to room temperature or warm in an oven pre-heated to 150ºC for 5-10 minutes.