THE RECIPE
WHITE ONION TARTE TATIN WITH MUSTARD SEEDS
Serves 6
Preparation time 2 hours (including set aside time)
Cooking time 30 minutes
INGREDIENTS
12 white onions, unpeeled
50g unsalted butter
2 thyme sprigs
2 bay leaves
15g unrefined cane sugar
100g wholegrain mustard
Fleur de sel
Double cream, to serve
Peppery baby salad leaves, to serve
For the shortcrust pastry (pie dough)
1 egg yolk
20ml whole milk
200g strong white bread flour
4g fine salt
1 tsp unrefined cane sugar
150g cold unsalted butter, cubed
METHOD
1. Make the shortcrust pastry. In a bowl, combine the egg yolk and milk. In another bowl, mix together the flour, salt, sugar and butter. Add the egg yolk and milk mixture to the dry ingredients. Bring together and knead the dough without working it too much. Shape into a ball, cover with cling film (plastic wrap), and set aside for at least 2 hours in the refrigerator.
2. Preheat the oven to 180°C/350°F/gas 4. Wrap each onion in a piece of aluminium foil and place on a baking sheet. Bake the onions for about 1 hour, until caramelised. Let cool, then peel and cut in half.
3. Heat the butter with the thyme and bay leaf in a wide sauté pan over medium heat until foaming. Add the halved onions and cook until golden brown.
4. Sprinkle the base of a 24cm ovenproof frying pan or skillet evenly with sugar. Arrange the roasted onions on it, packing them in tightly. Spread with the mustard.
5. Using a rolling pin, roll out the dough on a floured work surface to 2.5mm thick. Cut out a circle slightly larger than the bottom of the ovenproof frying pan or skillet and then cover the onions with the pastry. Pierce in places to let steam escape while cooking.
6. Cook for 5 minutes on the stove over low heat, then bake in the oven for 25 minutes, until the pastry is golden. Remove the tart from the oven and turn out onto a wire rack. Just before serving, sprinkle with fleur de sel and serve with the cream and salad leaves.
Bertrand Grébaut is chef and co-owner at Septime in Paris, La Cave, Clamato & D’une île