Melt butter and sugar in a pan over low heat until dissolved.
Add condensed milk and stir continuously until the mixture thickens into caramel.
Preheat the oven to 170°C.
Cream the butter and sugar in a bowl until light and fluffy.
Sift in the cornflour and plain flour and knead gently into a ball.
Line a 20cm x 30cm baking tin with parchment paper.
Press two-thirds of the dough into the bottom of the tin.
Spread three quarters of the caramel over the dough base.
Layer sliced bananas over the caramel and crumble the remaining dough on top.
Bake for 20 minutes until the top is golden-brown.
Cool in the tin for five minutes before cutting into squares.
Serve warm with banana ice cream, caramel sauce, and fresh mint.