Cream the butter and brown sugar, I use a stand mixer for this you want the butter to lose its yellow colour and for the creamed butter and sugar to almost look light and fluffy.
Add the egg and vanilla extract and beat until well combined.
Add the salt, flour and baking powder, and mix until combined.
Add the white chocolate chips and fold into the cookie dough.
Form the cookie dough into a log and wrap it in cling film. Chill in the refrigerator or freezer until nice and solid, but still able to be sliced through.
Preheat your oven to 180 degrees Celsius (360 F)
Unwrap the chilled cookie dough and roll in the Christmas sprinkles.
Slice the cookie dough into 1cm slices and lay on a baking paper lined tray.
Bake your cookies for 10-12 minutes, you want them to be quite blonde, not too golden. Allow them to cool on the trays for 5-10 minutes before transferring to a cooling rack.
Enjoy.