First sift the flour with the pinch of salt into a large bowl, holding the sieve up high to give it a good airing. Then add the lard and butter and, using only your fingertips, lightly rub the fat into the flour, again lifting the mixture up high all the time. When everything is crumbly, coarsely grate the goats' cheese in and then sprinkle in some cold water – about 1 tablespoon. Start to mix the pastry with a knife and then finish off with your hands, adding a few more drops of water, till you have a smooth dough that will leave the bowl clean. Then pop the pastry into a polythene bag and let it rest in the refrigerator for 30 minutes.
Meanwhile, pre-heat the oven to gas mark 5, 375°F (190°C) and pop the baking sheet in to pre-heat on the centre shelf.
Now prepare the leeks. First take the tough green ends off and throw them out, then make a vertical split about halfway down the centre of each one and clean them by running them under the cold-water tap while you fan out the layers – this will rid them of any hidden dust and grit. Then slice them in half lengthways and chop into ½ inch (1 cm) slices.
Next, in a medium-sized frying pan, melt the butter over a gentle heat and add the leeks and some salt. Give it all a good stir and let them cook gently, without a lid, for 10-15 minutes or until the juice runs out of them. Then you need to transfer them to a sieve set over a bowl to drain off the excess juice. Place a saucer with a weight on top of them to press out every last drop.
By this time the pastry will have rested, so remove it from the fridge and roll it out into a circle on a lightly floured surface. As you roll, give it quarter turns to keep the round shape and roll it as thinly as possible. Now transfer it, rolling it over the pin, to the tin. Press it lightly and firmly over the base and sides of the tin, easing any overlapping pastry back down to the sides, as it is important not to stretch it.
Now trim the edges and press the pastry up about ¼ inch (5 mm) above the rim of the tin all round, then prick the base all over with a fork. After that, paint some of the beaten egg for the filling over the base and sides. Now place the tin on the baking sheet and bake for 20-25 minutes or until the pastry is crisp and golden. Check halfway through the cooking time to make sure that the pastry isn't rising up in the centre. If it is, just prick it a couple of times and press it back down with your hands.
While the pastry case is pre-baking, crumble the goats' cheese with your hands, then gently combine it with the leeks in the sieve. Now, in a jug, mix the beaten eggs with the crème fraîche or double cream, seasoning with just a little salt (there is some already in the leeks) and a good grinding of freshly milled black pepper.
As soon as the pastry case is ready, remove it from the oven, arrange the leeks and cheese all over the base and then sprinkle the spring onions over the top. Now gradually pour half the cream and egg mixture in to join them, then put the tart back on the baking sheet with the oven shelf half pulled out, then slowly pour in the rest of the mixture. Gently slide the shelf back in and bake the tart for 30-35 minutes, until it's firm in the centre and the surface has turned a lovely golden brown.
Next, remove it from the oven and allow it to settle for 10 minutes before serving. This 10 minutes is important as it will be much easier to cut into portions. The best way to remove the tart from the tin is to ease the edges from the sides of the tin with a small knife, then place it on an upturned jar or tin, which will allow you to carefully ease the sides away.
Next slide a palette knife or wide fish slice underneath and ease the tart on to a plate or board ready to