|For the pastry|
|Plain flour||12 Ounce (350 Grams)|
|Cold butter||8 1⁄2 Ounce, chopped into small chunks (225 Grams)|
|For the filling|
|Butter||4 Ounce (100 Grams)|
|White wine vinegar||2 1⁄2 Fluid Ounce (75 Milliliter)|
|Soft light brown sugar||1 1⁄2 Tablespoon|
|Dijon mustard||3⁄4 Teaspoon (Heaped Teaspoon)|
|Maldon salt||2 Teaspoon|
|Vegetarian parmesan style cheese||2 Ounce, freshly grated (50 Grams)|
|Salad leaves||4 Ounce, dressed (100 Grams, To Serve)|
1. For the pastry, put the flour into a food processor and blitz with the butter, when the mixture is in fine crumbs, start adding the egg yolks, one by one. when all appears combined, bring it together with your hands on the work surface, but not kneading it. Wrap in cling film and rest it for 2 hrs in the fridge.
2. Peel and dice the onions as small as you can. The finer you chop them, the better the texture of the tart. Take a large pan,
with a lid, and melt the butter over a medium heat before adding the onions. They should cook slowly, with the lid on, needing the occasional stir. You want them completely soft before you start adding any more of the ingredients. This will take about 2 hrs.
3. Heat the oven to 200C/180C fan/gas 6 and grease a 27cm tart tin. When the onions are totally and pathetically soft, add the vinegar, sugar, mustard and the salt. The vinegar will take some time to evaporate but check the onions regularly; once the vinegar is gone they will begin to catch as the sugar starts
to caramelise. Keep on stirring at regular intervals and adjust the heat so that the onions turn a rich brown, but do not burn. A little colour from the bottom of the pan is okay, just stir it in. The vinegar/sugar stage will take approximately half an hour. When done, put the onion mix to one side.
4. On a lightly floured surface, roll out the pastry to the thickness of a £1 coin, and lay it across your tart case. Make sure the pastry is nicely tucked into the base. Leave the pastry overhanging the sides of the tart. Cover the pastry with a sheet of baking paper or foil before pouring in ceramic baking beans, or dried pulses. Bake in the oven for 25-30 mins, until uniformly golden all over and firm, with no dampness. Remove the foil or paper and beans and cook for another 5 mins.
5. Take the baked tart case out of the oven and allow it to cool. Carefully snap off the overhanging pastry. Neaten up the rim if you're fussy. Fill the case with the onion mixture and smooth it out evenly with a spatula. Sprinkle with the grated cheese, and go over with a good grind of pepper before returning it to the oven for a final 10 mins. Slice and serve with a few salad leaves on the side.