1.Preheat oven to moderate, 180°C. Line 18 holes of 2 x 12-hole muffin pans with paper patty cases.
2.In a large bowl, using an electric mixer, cream butter and sugar together until light and fluffy. Add eggs, one at a time, beating well after each addition.
3.Sift flour and mixed spice together. Fold lightly into creamed mixture with banana, sour cream and milk.
4.Spoon evenly into patty cases until ⅔ full. Bake for 20-25 minutes or until a skewer inserted in the centre comes out clean and dry. Cool in pan for 5 minutes. Transfer to a wire rack to cool completely.
5.To make passionfruit glaze icing, in a heatproof bowl, combine icing sugar, passionfruit pulp and butter. Place over a saucepan of simmering water. Stir until combined and icing is smooth. Spread evenly over cakes.
6.Top cupcakes with sprinkles to serve.