for the filling
4 large white onions, peeled and thinly sliced
about 800g when peeled
2 tablespoons olive oil
a generous sprig of thyme
6 large eggs, plus 1 beaten for egg wash
350ml double cream
150g aged cheddar, grated
salt & pepper
for the pastry
220g plain flour
110g butter, cut into small cubes
a large pinch of salt
1 egg yolk
Or a quantity of ready made pastry
to line a 25.5cm/10" pastry tin,
about 300g - 350g
Melt the butter with the olive oil in a large heavy bottomed pan. Add the onions and a pinch of salt and stir until the onions are well coated.
Add the thyme. Cover the pan and cook on a gentle heat until the onions are softened but not coloured, for around 30 minutes.
Remove the lid and continue cooking to evaporate the liquid for another 30 minutes or so, stirring occasionally. Take off the heat and allow to cool.
Now make the pastry. Sift the flour into a large bowl with the salt and quickly rub the butter into the flour. Add the egg yolk and enough ice-cold water to form a firm dough, about 1-2 tablespoons.
Form into a ball, cover with cling film and chill in the fridge for at least 30 minutes.
Set the oven to 190ºC.
On a lightly floured surface, roll out the pastry into a circle large enough to fit a loose bottomed pastry tin 25.5cm/10" in diameter and 3cm deep.
Place the pastry in the tin, pressing gently into the sides. Leave the excess to overhang. Line with greaseproof paper and baking beans and bake for 15 minutes. Remove the greaseproof and beans and bake for a further 5 minutes. Take the case from the oven and brush the whole of the inside with egg wash. Turn down the oven to 180ºC.
Beat the eggs and add the cream. Stir in the cheese and season well. Mix with the cooled onions and pour into the pastry case.
Return to the oven and bake for 10 minutes.
Turn the heat down to 160ºC and bake for a further 40 minutes, until the top is golden brown.
Remove from the oven and cool until set. Trim the edges or leave them untidy.