1.Preheat oven to 180ºC (160ºC fan-forced). Line eight holes of 12-hole (⅓-cup/80ml) muffin pan with paper cases.
2.Sift flour into small bowl, add remaining ingredients; beat with electric mixer on low speed until ingredients are combined. Increase speed to medium; beat until mixture is smooth and changed to a paler colour.
3.Divide mixture into paper cases. Bake about 20 minutes. Stand cakes in pan for 5 minutes before turning, top-side up, onto wire rack to cool.
4.To make buttercream, beat butter in small bowl with electric mixer until as white as possible; beat in sifted icing sugar and milk, in two batches. (To make chocolate buttercream, sift 2 tablespoons cocoa powder in with the icing sugar). Ice cakes according to directions of chosen cakes.
5.Smooth a generous amount of buttercream over top of cake. Sprinkle with brown sugar. Using a small sharp knife, thinly slice a small piece from a licorice allsort to make beach mat; top with jelly baby. Gently push paper cocktail umbrella into cake.