Pre-heat the oven-180Fan/200C/Gas6
Take the wedge of brie & cut 2 long slices from either side, then chop the rest into cubes. Set aside
Make the pastry case.
Roll out the pastry to about the thickness of £1 coin.
Use the pastry to line a 20cm loose bottomed tart or cake tin. Line with foil or baking paper then fill with baking beans or dried beans or/rice.
Chill the pastry in the fridge for 30 mins to prevent it from shrinking while cooking.
Remove the pastry case from the fridge, place the tin

Meanwhile melt the butter in a large frying pan over medium heat, add the leeks & cook until soft but not browned. Place the cooked leeks onto some kitchen paper.
Whisk together the milk, cream & egg yolks. Season well with salt & pepper & set aside.

Remove the pastry case from the oven.
Take out the beans & return to the oven for a further 5 minutes.
Remove the case from the oven & allow to cool for a few minutes.
Arrange the leeks evenly in the bottom of the pastry case then place the cubes of brie on top.
Carefully pour over the the cream & egg mixture.
Put the long strips of brie that you set aside on top to make a cross.
Bake for 25-30 minutes until the filling is set.
Serve warm or cold.