We tumbled through the door of the packed antique brasserie just opposite the Cathedrale Notre Dame de Strasbourg, our faces flushed from the frosty air and the glasses of gently spiced vin chaud bought from the Christmas market, one of the oldest in Europe. Laughing, perhaps a little too loudly, we grabbed the only remaining table positioned under misty windows illuminated with reflected candlelight. How many times has this little place witnessed the merriment of Christmas Eve we wondered. Everything finally in place and just the feasting to look forward to. And what a feast we had planned but first, a bottle of wine to share and a slice of this beautifully soft and creamy tart, a local delicacy of Alsace. The snow came on the way home and the perfect Christmas welcomed us into its loving arms.
For the pastry:
225g good quality plain flour
Half tsp salt
130g cold unsalted butter, cubed
1 egg yolk
1-2 tbsp ice cold water
For the filling:
60g salted butter
800g brown onions, very finely sliced
200ml double cream
4 egg yolks, beaten
Freshly grated nutmeg
1 tbsp fresh tarragon, finely chopped
45g Gruyère cheese, finely grated
Sea salt flakes and freshly ground mixed peppercorns
How I make it
To make the pastry, put the flour, salt and butter in a food processor and pulse until the mixture resembles breadcrumbs. Transfer it to a bowl, add the egg yolk and just enough of the water to bring the dough together. Place onto a floured surface and roll out enough to line a 25cm loose bottomed tart tin allowing the excess pastry to trail over the edge of the tin. Place in the fridge for half an hour.
Meanwhile, heat a large frying pan over a medium heat and add the butter. When it has melted, add the onions to the pan, cover and leave to caramelise for 30 minutes, stirring every 10 minutes. Remove from the heat and stir in the cream and egg yolks. Add the very small amount of nutmeg and the tarragon. Season to your taste and set aside.
Heat an oven to 180C.
Cover the pastry case with a sheet of baking parchment and fill with dried beans. Bake in the oven for 10 minutes. Remove the beans and return the case to the oven for around four minutes to allow the pastry to dry out.
Trim the excess pastry from the sides to leave a neat edge to your tart.
Pour in the prepared filling, sprinkle over the grated Gruyère and bake until set and golden on the top. Place on a cooling rack and eat just warm or at room temperature with a classic green salad and, if you’re feeling particularly hungry, a tumble of buttery new potatoes.