Using an electric mixer beat butter and sugar until light and fluffy.
Add eggs one at a time, beating well with each addition, then stir in dry ingredients, sour cream, milk and banana. Stir until smooth.
Transfer mix to a greased and lined 15x25cm loaf pan or large bundt pan and bake for 40 - 50 mins until golden. Cool in pan for 5 mins then transfer to a wire wrack to cool.
Mix icing sugar and passionfruit into a small bowl, using enough passionfruit to make a thick pouring consistency. Drizzle over completely cooled cake. Stand until icing dries a little then serve and enjoy!