Preheat the oven to 350°F / 180°C / Gas Mark 4.
Fry the onion in the remaining oil until golden and add to the meat.
Roll out the pastry and line a 20cm flan ring.
Bake the pastry case blind* in the oven for 10 minutes.
Place the leftover vegetables, bacon and cheese (if using) into the pastry case.
In a bowl, mix together the beaten eggs, cream, milk and herbs. Season well.
Pour this mixture on top of the vegetables.
Bake in the oven for 30 - 40 minutes (until set).