Measure all the ingredients into a large bowl and mix with a hand-held electric mixer until evenly blended.
Spoon the mixture into the prepared tin, scraping the sides of the bowl with a plastic spatula to remove all of it. Spread the mixture gently to the corners of the tin and level the surface with the back of the spatula.
Bake for 40–45 minutes, until the brownies have a crusty top and a skewer inserted into the centre comes out clean.Cover loosely with foil for the last 10 minutes if the mixture is browning too much. Allow the brownies to cool in the tin and then cut into 24 squares. Store in an airtight tin.