Preheat oven to 180°C (160°C fan-forced). Grease and line a 22cm cake tin.
Beat butter and sugars until pale and fluffy. Add eggs, one at a time, and beat until just combined.
Add mashed banana and vanilla and mix until combined.
Sift together flour, bicarbonate and salt together and stir through with milk until well combined and mixture attains a dropping consistency.
Spoon cake batter into prepared cake tin and smooth the top. Bake in pre-heated oven for 40 mins or until well risen and coming away from the sides of the tin. Test with a skewer to see if it is cooked – the skewer should come out clean.
Remove cake from oven and stand 5 minutes in the tin before turning it onto a wire rack to cool.
While cake is baking place icing ingredients in a small bowl over a saucepan of simmering water and mix thoroughly until a smooth paste forms and the correct glazing consistency is reached.
Pour glace icing over slightly warm cake –it should drizzle down the sides