Preheat the oven to 180°C/160°C fan/Gas mark 4.
Line your 9" x 9" cake tin with greaseproof paper.
Cream your softened butter and sugar together until soft and pale in colour, this will take about 4 minutes with a stand mixer, start with a low setting the increase to a medium once the ingredients are incorporated.
Sift in the both of the flours and salt into the mixture.
Beat together briefly until the it starts to come together as a dough, but is still a bit crumbly. Then bring together by hand, but don't knead or over mix, you want the dough to just be incorporated.
Put the dough into your prepared tin, I find it easer to do this by dotting bits of it over the based first so that I know it is evenly spread, then pressing it down by hand and finally smoothing out with the back of a metal spoon.
Bake in the centre of the oven for 25-30 minutes until just starting to become golden all over.
Leave in the tin to completely cool before adding your caramel sauce.