pre heat the oven to 180 and place a baking tray in to keep nice and hot

get your pre ready pastry case and set aside till later

rinse the lemons,then grate the zest in a heat proof bowl

add the juice from the lemons and the cornflour and stir to make a smooth paste.

put the water in a pan and bring it up to boil,when boiled pour it in to the lemon mixture stirring constantly with a wooden spoon.

when thoroughly combined pour the mixture back into the pan and cook stirring constantly untill it boils and thickens. reduce the heat and simmer for a minute.

remove the pan from the heat and beat in the 3 egg yolks,quickly followed by the sugar and butter. spoon the filling into the pastry case and spread evenly.

to make the meringue topping, put 4 egg whites in a large bowl and whisk until they stand in soft peaks.

gradually whisk in the sugar to make a stiff,glossy meringue.

pile the meringue on top of the lemon filling so its totally covered.

stand the tart on the hot baking tray and bake for 20mins or untill the meringue is golden Brown. leave to cool and serve at room temperature.