Preheat the oven to 350F (180 degrees C).
Grease a large cookie sheet with the oil.
Sift the flour and baking powder together.
Add the castor sugar, or for a really light texture use icing sugar.
Rub in the softened butter using your fingers to obtain a light crumbly texture.
Add the dried fruit.
In a small jug mix the egg with the tablespoon of milk.
Add the mix to the dry ingredients. In the beginning you will think that it is too dry but resist the urge to add more milk - as you mix the crumbly particles will start to come together. If you add too much milk the rock cakes will tend to spread instead of retaining their rounded rock-like shapes. I should know - I did this and they looked like flat choc chip biscuits – I may also have added too much sugar.
Divide the dough into half and then each half into half again so you have 4 roughly equal balls of dough. Divide each ball into five little rock cakes making sure they retain a rough texture rather than smoothing them into balls. Space them evenly on the cookie sheets allowing some room for spreading.
Bake for around 12 to 15 minutes.
Cool on a wire rack, or serve straight from the cookie sheets onto plates – they taste really good warm but the next day they are just as yummy.