For the pastry, rub the butter into the flour, then the egg. Combine the mixture until it comes together into a dough. Wrap it in cling film and chill it in the fridge
For the filling, cook the leeks and onion in a pan on a medium heat along with the butter, allspice and salt. Once the onions and leeks are soft, take them off the heat to cool slightly
In a bowl whisk up the eggs, the parmesan and 95ml of the single cream
In a food processor whizz up the cooked onions and leeks along with 100ml of the single cream
Add the onion mixture to the egg mixture, and then add the sage leaves. Set the filling aside
Pre-heat your oven to 200C/400F/Gas Mark 6
Roll out the pastry between two sheets of cling film. Line a 20cm loose bottomed pie tin and trim the edges
Line the pastry with baking paper and add baking beans. Blind bake the pastry case for 10 minutes. Remove the baking paper and beans and bake the pastry case again for 7 minutes at the same temperature
Remove the pastry from the oven and reduce the temperature to 160C Fan/180C/350F/Gas Mark 4
Fill the pastry case with the filling, arrange slices of the brie on top and sprinkle with some more fresh sage. Bake for 35 minutes until golden brown