Name: Onion tart
Total time: 1 h 15 min
Yield: Serves 4
Ingredients: 100g butter, cold; 175g plain flour; 50g gruyère cheese, finely grated; 1 egg yolk, beaten with 2 tbsp ice-cold water; 50g butter; olive oil; 800g onions, peeled and finely sliced; 2 sprigs thyme; 2, plus 1 yolk eggs; 150ml single cream; to serve bitter leaf salad

An onion tart next to a plate of salad on a black table

100g butter
cold
175g plain flour
50g gruyère cheese
finely grated
1 egg yolk
beaten with 2 tbsp ice-cold water

TART FILLING

50g butter
olive oil
800g onions
peeled and finely sliced
2 sprigs thyme
2, plus 1 yolk eggs
150ml single cream
to serve bitter leaf salad

Method

step 1
First make the pastry. Cut the butter into cubes and rub into the flour with your fingertips (or pulse in a food processor) until the mixture resembles fine breadcrumbs. Stir in a pinch of salt and the cheese.Add the egg yolk and water and mix with a knife or blend until bound. Wrap in clingfilm and rest in the fridge.
step 2
To make the filling, melt the butter with 2 tbsp olive oil in a large, heavy pan. Add the onions and fry gently until they are soft and beginning to colour. This will take about half an hour then leave to cool. Heat the oven to 200C/fan 180C/gas 6, roll out the pastry and use it to line a buttered deep sided 20cm or a shallow 23cm tart tin. Cover the base with greaseproof paper, fill with baking beans and bake for 15 minutes. Remove the paper and beans and cook for 5 minutes more.
step 3
Strip the thyme leaves from their stems and add to the onions. Mix the eggs, egg yolk and cream and season. Pour into the pastry case and cook for 15-20 minutes, or until the the tart is wobbly but just cooked. Serve with a bitter leaf salad.