1.Preheat oven to 180°C. Grease a 24cm bundt pan well; dust with flour, shake out excess.
2.Beat butter, sugar and extract in a small bowl with an electric mixer until light and fluffy. Beat in eggs, one at a time. Beat in mashed banana. Transfer mixture to a large bowl. Stir in sifted flour and soda, then milk. Spread mixture into pan.
3.Bake cake, on lower shelf in oven, for 30 minutes. Cover loosely with baking paper; bake for a further 10 minutes or until a skewer inserted into the cake comes out clean. Stand cake in pan 10 minutes before turning, top-side up, onto a wire rack to cool.
4.Beat mascarpone and cream in a small bowl with an electric mixer until soft peaks form.
5.Split cold cake into three layers. Whisk caramel in a small bowl. Spread bottom layer of cake with one-third of the caramel, then half the mascarpone mixture and half the banana slices. Repeat next layer with half the remaining caramel, remaining mascarpone mixture and remaining banana slices. Replace top of cake.
6.Whisk remaining caramel with the water; drizzle over top of cake.
Plain banana cake suitable to freeze. Not suitable to microwave. Top n Fill is a very thick caramel filling available in supermarkets.Note