MAKE THE BASE

Line a 9x13 inch (23x33cm) tin with baking paper, leaving overhang on two sides for easy lifting.

Crush digestives to fine crumbs using a food processor or by placing them in a bag and bashing with a rolling pin. Mix with melted butter until the mixture resembles wet sand.

Press firmly and evenly into the tin using the back of a spoon or the bottom of a measuring cup. Refrigerate for 15 minutes while you prepare the filling.

MAKE THE BANANA CARAMEL (No cooking required)

Spoon the tinned caramel into a mixing bowl. Add the banana powder and salt.

Whisk vigorously until the powder is completely incorporated and no lumps remain. The mixture should be smooth, thick, and taste distinctly of banana.

Taste and adjust—add more banana powder for stronger flavor if desired.

Spread evenly over the chilled biscuit base. The caramel should hold its shape and spread without running. Refrigerate for 30 minutes until firmed up.

ADD THE CHOCOLATE TOPPING

Melt chocolate with oil in 30-second microwave bursts, stirring between each, until completely smooth. Alternatively, melt in a heatproof bowl over a pan of simmering water.

Pour the melted chocolate over the caramel layer, tilting the tin gently to spread it into an even layer.

Sprinkle immediately with flaky sea salt (and banana chips if using) while the chocolate is still wet.

Refrigerate for at least 1.5 hours until chocolate is completely set.

CUT AND SERVE

Using the paper overhang, carefully lift the whole slab out of the tin and transfer to a cutting board.

Cut into bars using a sharp knife—run the blade under hot water and wipe dry between cuts for clean edges.

Store in the refrigerator for up to 1 week.