1 hour 20
Mash some of the soft onion and egg filling with a fork.
Let the tart cool (or even serve up cold) as that will mean the egg mixture will have set and it's easier to chop into finger-sized chunks.
225g plain flour, plus extra for dusting
125g butter, cubed
30g Parmesan cheese
1 medium egg, beaten
For the filling:
A knob of butter
1 tbsp olive oil
500g onions, thinly sliced
4 large eggs
300ml double cream
200g Gruyère cheese, grated
30g Parmesan cheese, grated
Salt and black pepper
The slowly caramelised onions give this tart a slight sweetness to add to the flavours from the cheese
Line a 24–25 cm deep round loose-bottom tart tin.
To make the pastry, put the flour, butter and Parmesan in a food processor. Whizz until it looks like breadcrumbs. Add the egg and 1 tablespoon of water and whizz until the mixture forms a ball. Roll out on a clean, lightly floured work surface and line the base and sides of the flan tin with the pastry. Set aside to chill in the fridge for 30–35 minutes.
Preheat the oven to 220°C/Gas 7. Prick the base of the flan pastry and line with baking paper and then baking beans. Blind bake the pastry for 10 minutes. Remove the beans and bake for a further 8–10 minutes until lightly golden, then place the pastry case on a baking sheet.
To make the filling, melt the butter and olive oil in a frying pan. Add the onions and fry over a medium–high heat for five minutes. Cover with a lid and gently simmer for 20 minutes until soft and golden brown. Spread onto the base of the tart.
Beat the eggs in a bowl. Add the cream and milk and season. Add the Gruyère, then pour into the case. Sprinkle with the Parmesan.
Reduce the oven to 180°C/Gas 4. Bake for about 30–35 minutes until lightly golden on top and set in the middle.
This recipe is taken from Annabel’s Family Cookbook by Annabel Karmel (Ebury Press, £20). Photographer: Martin Poole