Place the flour into a mixing bowl, add the salt, mustard and herbs and mix through. Cut up the butter into small pieces , stir through the butter and rub in with cool fingertips. Stir in the egg yolk 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 24cm 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.
Saute the leeks in the butter until soft. Stir in the flour and mustard powder. Gradually stir in the milk off the heat and then thicken back on the heat stirring all the time. Remove from the heat and stir in the goats cheese and eggs. Spoon into the prepared baked pastry shell. Top with the hard cheese mixed with the breadcrumbs.
Bake at 200c/400f/gas 6 for 20 minutes until golden.
Pastry Case
Rarebit filling