For the pastry, rub the butter into the flour until it resembles course breadcrumbs then, using your hands, add just enough beaten egg to bring it together.

With your hands, flatten out the ball of dough until it is about 2cm thick, then wrap in cling film or place in a plastic bag and leave in the fridge for at least 30 minutes or, if pushed for time, in the freezer for 10-15 minutes.

Remove the pastry from the fridge and place between two sheets of cling film (larger in size than the tart tin). Using a rolling pin, roll the pastry out to no thicker than 5mm or even thinner for small tartlet tins. If the tin is round, make sure to keep the pastry in a round shape and also large enough to line the base and side of the tin.

Remove the cling film and place into a 18cm quiche tin (with3cm high sides). If you wish, retain the top layer of cling film to help shape the pastry. Press the pastry into the edges and, using your thumb, "cut" the pastry along the edge of the tin for a neat finish. Remove the cling film, if used, prick over the base with a fork and chill the pastry in the fridge for 30 minutes or the freezer for 10 minutes. (Or cover it back up and keep in the freezer for a few weeks).

Preheat the oven to 180C/350F/Gas 4.

Line the pastry with foil, greaseproop or partchment paper, leaving plenty to come up the sides. Fill with baking beans or dried pulses. Place in the oven and bake for 15-20 minutes, or until the pastry feels dry.

For the filling, heat the oil in a frying pan and cook the bacon until crisp. Remove and set aside to drain on kitchen paper. Fry the onions gently in the same oil for a further 20 minutes. Meanwhile, whisk the eggs in a medium sized bowl, add the cream, herbs, cheeses and bacon and onions. Mix well and add salt and freshly ground black pepper.

Remove the pastry from the oven and remove the paper and beans, pour the filling into the pastry base and return to the oven for 30-40 minutes, or until the centre has just set. Serve warm.