Special equipment: 7 1/2-inch high-sided tart pan or 9-inch shallow quiche plate
Make the Shortcrust pastry, recipe below, leaving to chill for 30 minutes before using.
Preheat the oven to 350 degrees F. Line the tart pan with the pastry dough, and bake 'blind'.
Filling: Heat the oil in a frying pan and cook the bacon until crisp. Remove and drain on paper towels. Then sweat the onions gently in the same oil for 10 minutes more.
Meanwhile, whisk the eggs in a medium-sized bowl, add the cream, parsley and chives, cheeses, and cool bacon and onions. Mix well and add seasoning.
Pour the filling into the pastry base and return to the oven for 30 to 40 minutes, or until the center has set. Serve warm with a green salad and relish.
Put the flour, salt, and butter in a food processor and whiz or pulse briefly. Add half the beaten egg and continue to whiz. You might add a little more egg, but not too much as the mixture should be just moist enough to come together. If making by hand, rub the butter into the flour until it resembles coarse bread crumbs. Then, using your hands, add just enough egg to bring the dough together.
With your hands, flatten out the ball of dough, until it is about 3/4-inch thick, and then wrap in plastic wrap or place in a plastic bag and leave in the refrigerator for at least 30 minutes or, if you are pushed for time, in the freezer for 10 to 15 minutes.
Makes 1 crust (about 14 ounces).
Blind Baking. To pre-bake a pastry shell before adding filling, first chill the pastry, and then line your pan. Line the pastry with foil, parchment or greaseproof paper, leaving plenty to come up the sides. Fill with baking beans (alternatively, for a really smooth finish use plastic wrap to line the pastry: place 2 sheets over the pastry, add the beans and bring the edges into the center.) Whichever method you choose, bake 'blind' in a 350 degree F, oven for 15 to 20 minutes or until the pastry feels dry. Remove the paper and beans, brush with a little leftover beaten egg and return to the oven for 2 minutes. If there are any little holes or cracks in the pastry, just patch it up with any leftover raw pastry before you return it to the oven. Remove from the oven and set aside in the tin while you make the filling. The pastry can be baked a day in advance and kept covered until you need it. Variations: Sweet shortcrust pastry: In place of the pinch of salt, use 1 tablespoon of icing sugar. Sour cream shortcrust pastry: Replace the egg with 2 tablespoons of sour cream or creme fraiche, adding just enough to bring the dough together.