Preheat the oven to 130°C/250°F/Gas ½. Line a swiss roll tin 28cm x 18cm/11" x 7" with good quality baking parchment. Lightly brush with oil.
Warm the condensed milk in a large pan.
Meanwhile, mix together all the other ingredients and then add the warmed condensed milk. Mix well, making sure all the dry ingredients are moistened.
Spread the mixture evenly into the prepared tin. Press down well with the back of a spoon dipped in cold water.
Bake for about 1 hour, until golden brown and set. Remove from the oven and allow to cool a little before gently cutting into bars with a serrated/bread knife.
