This recipe for GF Flour Mix A is straight from my Phil Vickery cookbook. It can be used for cakes, biscuits, slices and a whole range of other baking that has needs for a lighter (and obviously gluten free) flour mix.
I will link to this recipe when needed.
700g fine white rice flour
200g potato flour
100g tapioca flour
Mix all the flours together very thoroughly or put into a food processor and pulse until mixed. Store in an airtight container.