Preheat oven to 180°C.
Lightly grease a 23cm quiche dish with butter and line with pastry. Trim excess. Line pastry with baking paper. Half-fill with rice or baking beans. Bake for 10 minutes. Remove paper and beans and bake for another 10 minutes
Heat a nob of butter along with a drizzle of olive oil in a frying pan over medium-high heat. Add onion. Cook until the onion on a low heat for 10 minute or until they have gone golden brown and caramelised. Spread the onion over the pastry
In a jug whisk the egg, cream and milk together then add the cheese and seasoning. Pour over the egg mixture over the onion.
Bake for 30 to 35 minutes or until set. Stand for 5 minutes. Serve.