- 170g plain white flour
- 70g unsalted butter, chilled
- 1 egg, beaten
- Sea salt
- 3 large white onions, sliced finely
- 50g unsalted butter
- 1 tsp caster sugar
- 2 egg yolks
- 150ml half-fat créme fraîche
- 2 sprigs fresh thyme, leaves only
- Freshly ground black pepper
1. Sift the flour with a good pinch of salt into a large bowl. Cut the butter into small cubes; coat in the flour, then rub into the flour with your hands until it resembles damp sand. Add the beaten egg and just enough iced water (2-3 tablespoons) to make a soft dough. Place into a small bowl, cover with a lid or a plate and chill for 30 minutes.
2. Preheat the oven to 200C/Gas 6.
3. In a heavy-bottomed pan, melt the butter. Add the onions and the sugar; cook for 30 minutes, stirring occasionally. Stir in the thyme and set aside.
4. Roll the dough on a floured surface until thin. Carefully place in a lightly buttered, 20cm tart tin (ideally one with a removable bottom). Line with greaseproof paper, add baking beans (or dried beans) and bake in the oven for 10 minutes. Take the pastry out of the oven and remove the paper and beans. Mix the egg yolks with the créme fraîche and some pepper. Drain any fat off the onions, spoon into the pastry case and spread the egg mix across the top. Turn the oven up to 190°C/gas 5 and bake for 25-30 minutes, until golden on top. Serve warm, cold or at room temperature – up to you, it's delicious any way you eat it!