Cream the butter until soft then beat in the sugars until well combined and a little paler - don't whip too much air in.
Beat in the egg fully then beat in the vanilla.
Sift the flour, salt and raising agents over the creamed mixture and stir in until few specks of flour remain.
Stir in the remainder of the ingredients - it will be quite stiff but don't worry, it will come together. Spatch into a greased and lined 8 inch square brownie pan and bake on 165˚C for 25-30 minutes - the top will be set and honeycomb coloured and a skewer will come out almost dry with a very few damp crumbs stuck to it.
Cool in the tin until room temp before attempting to lift out of the pan then slice into 9 rectangles.
Recipe Notes
*= or chop up a bar of Caramac if you are able to get it, failing that, I'd use muscavado sugar and replace the morsels with chopped white chocolate
Adapted from Doris Greenspan's book Baking: From My Home to Yours