Line two cookie trays with non-stick baking parchment.
Cream the butter, sugar and vanilla extract until pale and smooth.
Beat the egg with a fork and add to the butter mix gradually, beating well between each addition.
Sift in the rice flour, arrowroot, ground linseed and baking powder.
Add the ground almonds, stir into a smooth dough and add the chocolate chips.
Form the dough mixture into a sausage using cling film, chill until firm and slice into biscuits. You can store the cookie dough mix in the freezer for two months and just slice off when required.
Bake at 190ºC (180ºC fan) for 10 minutes until golden brown and firm to the touch.
The cookies will still be soft in the centre, but will crisp up a bit when they cool.