Mix the egg, water, oil and brownie mix together until well blended (mixture may be lumpy).
Divide the mixture (about 300g) evenly between the greased and lined loaf tins.
Bake in the centre of the oven for 10 minutes. Remove from the oven.
Mix the eggs, oil, water and cake mix gently together and whisk (by hand or electric mixer) for 2-3 minutes until smooth and creamy.
Divide the cake mixture evenly between the 2 loaf tins, gently spooning the mixture on top.
Bake in the centre of the oven for a further 30-35 minutes or until a rounded knife inserted into the centre of the cake comes out clean, then cool on a wire rack.
Bake Once the cake is cool, spoon over the icing then decorate with your sprinkles. Slice to serve.