Preheat the oven to 180°C/ 350°F/Gas mark 4. Lightly grease a loaf tin.
Beat together the cake mix, coconut, eggs, sour cream and milk for 3–4 minutes or until smooth. Pour the mixture into the loaf tin.
Bake for 45–50 minutes until the top is springy to the touch and a skewer inserted in the centre comes out clean. Turn onto a wire rack to cool, and serve cut in slices.