Place the flour into a mixing bowl, add the salt, cut up the butter into small pieces , stir through the butter and rub in with cool fingertips. Stir in the egg yolks and a little cold water to bring it into a pliable dough. .
Shape into a flattened disc and wrap in clingfilm and rest in the fridge for 30 minutes.
Roll out the pastry on a floured surface, the crust should be no more than 6mm/¼-inch thick and then used to line a flan tin which, in general, are no deeper than 4cm/1½-inches. Trim away excess pastry, line with a sheet of foil and baking beans. Chill for 30 minutes.
Bake blind for 15-20 minutes in a preheated oven at gas 6/200c/400f, remove from the oven, and remove the foil and beans. Reduce the temperature of the oven to gas4/180C/160C Fan for about 10-15 minutes until dry to the touch. Now you are ready to fill and bake your tart.
Brush the cooked pastry shell interior with the mustard.
Top with the cooked leeks.
Heat the milk in a pan, add the grated cheese, mustard and chilli powder and melt the cheese slowly over a low heat. Remove from the heat and stir in the flour. Mix well and return to the heat and thicken, stirring all the time. Remove from the heat and cool a little, then whisk in the eggs. Pour over the top of the leeks, top with a good crust of cheese and breadcrumbs and bake at 200c/180c Circotherm/gas 6 until bubbling and golden on top.
250g plain flour
¼ teaspoon sea salt
140g chilled butter
2 egg yolks
3-4 tablespoons chilled water
1 teaspoon Dijon mustard for the tart base
3 Medium leeks, trimmed, washed and finely shredded sautéed in 50g butter
150ml full fat milk
1 teaspoon mustard powder
1/4 teaspoon chilli powder
30g plain flour
200g full flavoured hard cheese
3 medium sized eggs
50g full flavoured hard cheese mixed with 2 tablespoons of breadcrumbs and 1 tablespoons chopped herbs.