To make the short crust
Place the flour, butter and salt in a food processor and pulse to a breadcrumb consistency. Add the water in a gradual stream; stop as soon as the dough comes together. Turn out and knead the dough a couple of times, then wrap and chill in the fridge for half an hour or so.
Pre-heat the oven to 180°C.
When you're ready, remove the pastry from the fridge and allow to come up to room temperature. Roll out the to about 3mm thick and line your tart case. Leave the edges over hanging. Prick the base with a fork then line the case with parchment and baking beans. Bake blind for about 20 minutes then remove the beans and return to the oven for a further 10 – 12 minutes or until the base is just golden. Set aside and leave the pastry to cool.
Melt the butter in a heavy based saucepan over a medium heat, add the sliced onions along with half the thyme leaves and plenty of salt and pepper. Give the onions a good stir and place a lid on the pan. Turn the heat down a little and cook stirring regularly for 20 - 25 minutes or until the onions are lovely and soft and beginning to caramalise round the edges. Spoon the onions out of the pan into a large mixing bowl, then return the pan to the heat. Add the bacon lardons and the remaining thyme and fry for 4 - 5 minutes or until just beginning to crisp. Combine the bacon, with the onions and the grated cheese and arrange over the base of the tart case. Whisk the whole eggs and yolk with the cream, milk and some salt and pepper. Pour the custard over that tart filling. Bake straight away at 180°C for about 20 minutes or until golden and slightly risen.
Allow it to cool before you eat it. It’s much better then.
Serve with Rosebud Ampleforth Abbey Beer Fruit Chutney.