The ultimate makeover: Onion tart

Ingredients

• 2 large onions red halved (550g 1lb 4oz total weight)
• 2 tbsp rapeseed oil 
• 2 medium eggs 
• 200 ml carton half-fat crème fraîche 
• 1 tsp thyme leaves 
• 1 tsp dijon mustard 
• 25 g gruyere cheese 
• 175 g self-raising flour 
• 25 g butter cold cut in small pieces
• 100 g natural yogurt 
• 4 tbsp semi-skimmed milk 

Equipment

• bowl
• frying pan
• baking sheet
• oven
• knife

Directions

1. Slice the onions into small, thin, wedge-shaped pieces.
2. Heat the rapeseed oil in a large, preferably non-stick, saut or deep frying pan. Stir in the onions and fry over a medium heat for about 20 mins. Stir only occasionally so they can cook fairly undisturbed and caramelise underneath. When done, they should be well caramelised and sticky.
3. Meanwhile, prepare the base.
4. Heat oven to 190C/170C fan/gas 5 and put in a baking sheet.
5. Put the flour and butter in a bowl with a pinch of salt and rub with your fingers until it resembles rough crumbs.
6. Mix the yogurt and milk, pour it into the flour mixture and work together briefly with a knife until the dough just comes together.
7. Remove from the bowl and gently press together to form a ball. Do not overwork the mixture.
8. Roll dough out thinly on a lightly floured surface and use to line a 23cm round, fluted, loose-based flan tin, about 2.5cm depth, pressing it with your fingers into the flutes. Sit the tin on. If the dough is a little sticky, dust your fingers in some flour.
9. Beat the eggs in a medium bowl, then stir in the crme frache, thyme, mustard and seasoning. Spoon and spread half of the onions into the lined base, season with pepper then scatter over half the cheese.
10. Pour the egg mixture over the top, then scatter over the rest of the onions and cheese. Sit the tin on the hot baking sheet and bake for 25-30 mins until the base and filling are cooked.
11. Remove and cool for about 10 mins, then remove from the tin and serve while fresh and warm.