Combine crushed digestive biscuits and melted butter in a mixing bowl and stir until well coated. Press the mixture evenly into the bottom of a 9-inch springform pan to form the crust. Bake at 180°C (350°F) for 10 minutes or until golden. Remove and let cool.
In a skillet over medium heat, sprinkle sugar over the sliced bananas and cook, stirring gently, until the sugar melts and begins to caramelize, turning the bananas golden brown. Add lemon juice and cook for another 2 minutes until thickened. Transfer caramelized bananas to a bowl and set aside.
Pour sweetened condensed milk into a heavy-bottomed saucepan and cook over low heat, stirring constantly, until it thickens and turns a golden caramel color—about 10-15 minutes. Remove from heat and let cool slightly. Spread the caramel over the cooled biscuit crust, then evenly layer the caramelized bananas on top.
Whip heavy cream with powdered sugar and vanilla extract using a mixer until stiff peaks form. Spread or pipe the whipped cream evenly over the banana layer, smoothing the surface for a clean finish.
Refrigerate the assembled cake for at least 2 hours to set. Before serving, optionally garnish with additional banana slices or chocolate shavings. Slice and serve cold, showcasing the layered textures and caramelized glazes.
