Preheat oven. Roll out one tin of crescent dough into an 8"x12 " tin. Press to seal any gaps in the dough. Place parchment paper over dough and then place a second tray onto dough (to stop the dough from rising too much while cooking).

Bake for 10 minutes or until golden. Repeat for second sheet of dough. Allow to cool on a wire rack.

To make the filling, place the milk, cream butter, vanilla and sugar in a saucepan over medium-low heat and cook until hot but not boiling (there should just be bubbles around the edge of the pot).

Mix the cornflour and water to a smooth paste and whisk into the hot milk mixture and then add the egg yolks and stir, allowing to simmer, for 6 minutes or until the mixture has thickened.

Remove from the heat allow to cool to room temperature. (Or in the fridge)

Place one of the pastry sheets in a 20c x 30cm slice tin lined with non-stick baking paper and spread over the filling then the remaining pastry and then refrigerate for 2 hours or until set.

For icing:
Mix powdered sugar, lemon juice and zest. Pour over slice and allow to set