• Add the butter and sugar to a bowl and mix with an electric whisk until light and fluffy.
• Add in the egg and vanilla extract and mix again.
• Sift in the flour and baking powder and mix until it comes together in a cookie dough. Add the chopped white chocolate and California walnuts and mix.
• Place the cookie dough into the fridge for 30 minutes to firm up. Once firm, using an ice cream scoop, scoop out 12 scoops of the mix and roll into balls.

If cooking now:

• Preheat the oven to 180°c. Place the cookie dough balls over two large lined baking trays giving them space to spread. Cook for 12-13 minutes until golden round the edge then remove from the oven and leave to sit for 20 minutes to firm up.

If making to freeze:

• Place the cookie dough balls in a labelled freezer bag and freeze flat.

Cooking from frozen:

• Preheat the oven to 180°c. Place the frozen cookie dough balls on a lined baking tray giving them space to spread. Cook for 14-16 minutes until golden round the edge then remove from the oven and leave to sit for 20 minutes to firm up.