Simply follow our simply laid out recipe:
1) To make the pastry, sift flour and salt together, add butter and rub in until mixture resembles fine breadcrumbs.
2) Mix to a firm dough with egg yolk and 4-5 tsp cold water.
3) Wrap and chill for 30 minutes.
4) For the filling, melt butter in a large pan and fry onions for 10-12 minutes until soft.
5) Leave to cool.
6) Preheat oven to 200°C, Gas 6.
7) Roll out pastry on a lightly floured surface and use to line a 23cm fluted flan tin.
8) Line pastry with greaseproof paper, add baking beans and bake blind for 15 minutes.
9) Lower oven temperature to 180°C, Gas 4.
10) Remove the baking beans and paper and return pastry case to the oven for 5 minutes.
11) Raise oven temperature back to 200°C, Gas 6.
12) Mix together the cooked onions, flour, eggs, cheese, cream and seasoning.
13) Add to the pastry case and cook for 25-30 minutes.
14) If you want to serve the tart warm, it will taste best if you allow it to stand for 15 minutes after removing from oven.