Cut off quarter of your pastry for the lid. Then, working quickly, roll out the remainder into a circle big enough to cover the base and sides of a 20cm springform cake tin. If you have a chopping board or baking sheet big enough, roll it out onto this. It will mean that you can put your tin upside down onto it and flip the whole lot over to get the pastry into the container. Otherwise, lift it into the tin. Make sure the pastry is pushed up against the sides with no air pockets.