Whiz biscuits in a food processor until finely crushed.
Melt half the butter. Add to the crushed biscuits and whiz until combined.
Divide the mixture among the tartlet cases. Use the back of a spoon to push down the base and up the sides evenly. Firm up in fridge until caramel is ready.
Melt sugar and remaining butter in a saucepan. Bring to simmer for 5 minutes.
Add condensed milk, stir to combine, and simmer for 10 minutes until you have a thickened, golden caramel.
Pour the caramel over the bases and set in fridge for 1 hour.
Arrange the sliced bananas over the set caramel tarts. Dollop the cream to cover each tart.
Notes
Add grated chocolate if desired. To save time, you could use pre-prepared caramel, but where's the fun in simply assembling a dish? You gotta cook something.