5 onions, cut in half and thinly sliced
1tsp fresh chopped thyme
120ml crème fraiche
2 egg yolks
100g wholemeal flour
70g plain flour
70g cold butter, chopped
2-3 tbsp iced water
Make the pastry by sieving the flours into a food processor together with the butter and pulse until mixture resembles breadcrumbs. Add beaten egg and process, adding water until mixture becomes a dough. Cover with cling film and refrigerate for at least 30 minutes
Whilst pastry is chilling, in a heavy bottomed pan with a lid, melt the butter over a medium heat and add the chopped onions and thyme to sweat, stirring occasionally. Do not let the onions brown. This should take about 30 minutes.
Preheat oven to 180°C. On a lightly floured board roll the chilled pastry thinly and line a 20cm tart tin with a removable bottom. Prick the base of the pastry with a fork and chill for another 20 mins. Line with baking paper and put in baking beans. Bake for 10 minutes.
Take pastry out of the oven and remove paper and beans. Mix the egg yolks and crème fraiche together and stir in onion mixture. Sprinkle feta over the top and return to the oven. Bake for 25-30mins until golden and set.