Place cherries, sugar, cornflour, lemon juice and vanilla extract in a mixing bowl. Stir to combine, then set aside for 10 minutes.
Roll out the first sheet of pastry. Place a 30cm (diameter) pie tin upside down on pastry and use a knife to cut around the edge. Turn the pie tin over and press the pastry circle into the bottom to form the base of your pie.
Spoon cherry filling into the pie tin. Then roll out your second sheet of pastry. Use a knife or pastry crimper to create 9 equal-width strips of pastry. Brush with beaten egg.
Place 5 strips running vertically down the top of your pie. Carefully weave the remaining strips horizontally over and under the vertical strips.
Bake for 15 minutes, then reduce heat to 180°C and bake for a further 20 minutes or until pastry is golden and filling is bubbling. Remove from oven and set aside to cool slightly before serving. The filling will thicken the more it cools.