Jo Pratt's Double Chocolate Freezer Cookies

Place the butter and sugar in an electric mixer or food processor and blend until pale and creamy. Add the vanilla extract and egg yolk and whizz briefly before sifting in the flour and cocoa powder. Mix until you have a smooth dough and then add the chunks of chocolate.

Using lightly floured hands, roughly roll the dough into golf ball-sized balls and gently press each one to a cookie shape in the palm of your hand. Place on a small, clingfilm-lined baking tray or something that will sit flat in your freezer.

Leave in your freezer for about 1 hour until the dough becomes solid, then peel away from the clingfilm. Place the cookies in a freezer bag to store for up to 2 months.

When you want to bake some of the cookies, preheat the oven to 200°C/gas 6. Remove as many as you wish from the freezer and place on a greased baking tray, leaving a small gap between them.

Bake for about 15 minutes until they are just beginning to firm up, but haven't become too dark around the edges. Remove from the oven, sprinkle the tops with the grated chocolate and allow to cool for a couple of minutes before cooling further on a wire rack.

The cookies can be cooked as soon as they are made. They will take just 10 to 12 minutes in the oven. These quantities will easily double up to allow you to make plenty for your freezer.