Preparation time: 20–25 minutes, plus chilling
Cooking time: 1¼ hours
For the pastry
200g plain flour, plus extra for dusting
pinch of salt
100g butter, plus extra for greasing
1 egg yolk
For the filling
4 onions, thinly sliced
2 tsp thyme leaves
225ml double cream
50g Gruyère cheese, grated
½ tsp fresh grated nutmeg
salt and pepper
1. To make the make the pastry. Sift the flour and salt together into a large bowl, dice the butter and add to the bowl, then rub with your fingers until the mixture resembles fine breadcrumbs. Add the egg yolk and just enough water to bind to a soft, but not sticky, dough. Roll into a ball, wrap in clingfilm and refrigerate for 15 minutes before using.
2. Preheat the oven to 180°C/350°F/Gas Mark 4. Roll out the pastry on a lightly floured surface. Press the pastry into a greased twenty centimeter loose based tart tin, lay a piece of baking paper on it, cover with baking beans and bake blind in the preheated oven for 15 minutes.
3. Remove from the oven and increase the oven temperature to 200°C/400°F/Gas Mark
6. Take out the beans and paper and bake the pastry case for a further five minutes. Leave the oven on.
4. To make the filling, melt the butter in a large, heavy based frying pan over a low to medium heat, then add the onions and thyme and fry gently,stirring frequently until lightly browned. This will take 15-30 minutes. Season with salt and pepper, remove from the heat and leave to cool for ten minutes.
5.Lower the oven temperature to 190°C/375°F/Gas Mark 5. In a large bowl, beat the eggs and cream together. Add the cheese, nutmeg and cooked onion mixture and stir. Pour the mixture into the pastry case and bake, uncovered, for 30–40 minutes, or until golden brown. Serve immediately
Recipe from The Bistro Cookbook part of Parragon Books range of Love Food cookbooks. Visit parragon.com/lovefood