1 quantity of shortcrust pastry
400g (14oz) onions, peeled and halved lengthways
30ml (2 tbsp) vegetable oil
15ml (1 tbsp) balsamic vinegar
2 eggs
1 egg yolk
200ml (7fl oz) milk
100ml (3½fl oz) crème fraîche
salt and freshly ground black pepper
50g (2oz) Roquefort cheese
30ml (2 tbsp) freshly grated
Parmesan cheese