Shortbread is a reliable biscuit to make and it stores well for when folk drop in for a cuppa. Easy to make and few ingredients, here is my mother's recipe which I have seen no need to deviate from.
For one disc which will cut into 8 decent portions, you will need;
165g of butter (see note)
80g of caster sugar
180g of plain flour
80g of rice flour
Begin by mixing the butter and sugar in a food mixer until you have a smooth and even paste, add the flours and continue to mix until you have a soft dough. Spill out onto a floured surface and shape into a disc, transfer to an 20cm loose bottomed cake tin and press to flatten, Dock by making holes in the disc with a wooden skewer. Leave to rest while the oven heats up to 140 to 150C, bake for 45 to 60 minutes. I like to bake the shortbread at a lower temperature than sometimes suggested and for a little longer to achieve a very pale but well dried out finish. Take the cake tin out of the oven and divide into triangles while still hot. Leave to cool completely before removing from the tin.
I suggest 140C to 150C because ovens vary and if like me, you wish the shortbread to be pale, keep an eye on the temperature and turn it down if the shortbread looks as though it's browning.
This is one of the few recipes where I use salted butter, but if you have only unsalted, add 1/2 a teaspoon of salt for this quanitity.
Having said that I see no reason to change the recipe, I do occasionally add lightly toasted whole hazelnuts, I then roll the dough up into a log shape, chill in the fridge for a couple of hours or so before cutting into 1cm individual biscuits and baking as above.