MAKE THE SHORTBREAD BASE
1. Preheat oven to 325°F (165°C / 145°C fan). Line a 9x13 inch baking pan with parchment paper, leaving overhang on the long sides for easy removal.
2. In a food processor, pulse together the all-purpose flour, rice flour, sugar, and salt until combined. The rice flour adds the characteristic sandy, melt-in-your-mouth texture of proper shortbread.
3. Add the cold cubed butter and pulse in short bursts until the mixture resembles coarse breadcrumbs with some pea-sized pieces remaining. Don't overprocess—some larger butter pieces create flakiness.
4. Tip the mixture into the prepared pan and press firmly and evenly across the bottom. Use the flat bottom of a measuring cup to compact it into a smooth, even layer about ½ inch thick.
5. Prick the shortbread all over with a fork to prevent puffing. Refrigerate for 15 minutes to firm up the butter.
6. Bake for 35-45 minutes until pale golden all over with slightly darker edges. The surface should look dry and matte, not shiny. Cool completely in the pan—at least 1 hour. The base must be completely cold before adding the caramel.

MAKE THE BANANA CARAMEL
7. In a heavy-bottomed saucepan, combine the butter, brown sugar, and golden syrup. Heat over medium-low, stirring constantly, until the butter melts and sugar dissolves completely.
8. Pour in the condensed milk and increase heat to medium. Bring to a gentle boil, stirring continuously. Never stop stirring once the mixture begins to boil, or it will catch and burn.
9. Add the mashed banana, vanilla, and salt. The mixture will bubble vigorously—this is normal. Continue stirring.
10. Cook and stir for 20-25 minutes. The caramel should thicken significantly, pull away from the sides, turn deep amber, and reach 240-245°F (116-118°C) on a candy thermometer—the soft ball stage. It should leave a clear trail when you drag a spatula through. This extended cooking evaporates the banana moisture for proper setting.
11. Immediately pour the hot caramel over the cooled shortbread. Spread evenly with an offset spatula, working from center outward.
12. Cool at room temperature for 30 minutes, then refrigerate for at least 1 hour until caramel is completely firm.

APPLY THE CHOCOLATE TOPPING
13. Melt the chopped chocolate with coconut oil in a heatproof bowl over simmering water (or microwave in 30-second intervals), stirring until smooth and glossy.
14. Pour the chocolate over the set caramel. Tilt the pan and use an offset spatula to spread evenly to the edges.
15. Immediately sprinkle the flaky sea salt over the wet chocolate. Add banana chips and gold leaf for decoration if using.
16. Refrigerate for at least 1 hour until chocolate is firm, or 2-3 hours for cleanest cuts.

CUT AND SERVE
17. Let sit at room temperature for 10 minutes to prevent chocolate cracking.
18. Using the parchment overhang, lift the slab onto a cutting board. Cut into 16-20 bars with a sharp knife dipped in hot water and wiped between cuts.
19. Stack at angles like Jenga pieces for Frances's signature presentation.