Caramelised onion tart

Method

1. To make the pastry, spoon the flour and salt into a food processor and pulse quickly to mix. Add the butter and pulse until it’s the texture of fine breadcrumbs. Stir through the egg yolk and 1-2 tbsp iced water, adding it a little at a time until the pastry just starts to come together. Shape into a disc, wrap in cling film and chill for 30 minutes.
2. Meanwhile, heat the oil and butter in a large sauté pan. When it foams, add the onions, season, cover and cook over a low heat for 30 minutes until soft. Remove the lid and cook for 10 minutes to evaporate the liquid. Add the sugar and cook for a further 5 minutes until the onions start to caramelise. Set aside to cool.
3. Preheat the oven with a baking sheet inside to 220°C/fan200°C/gas 7. On a lightly floured work surface, roll out the pastry to line a 29cm x 19cm x 3cm loose-bottomed fluted tart tin. Prick the base all over and chill for a further 20 minutes.
4. Line the pastry base with baking paper, fill with baking beans or rice and blind-bake for 12 minutes. Mix the egg and yolks with the cream and cheese and season with salt and freshly ground black pepper. Remove the paper and beans/rice, then return to the oven for 5 minutes. Remove the pastry shell from the oven and turn it down to 180°C/fan160°C/gas 4.
5. Spread the mustard over the base of the pastry. Fold the thyme leaves through the onions and spoon over the top, then pour over the cheese and cream mixture, grate over the nutmeg and top with a few small sprigs of thyme. Bake for 30-35 minutes until just set and serve warm or cold with a crisp salad.