Preheat your oven to 160°C (320°F). Line your baking tin with parchment paper for easy removal.
In a mixing bowl, cream together the butter and golden caster sugar until the mixture is light, fluffy, and smells subtly nutty—that’s about 3-4 minutes with a hand mixer or vigorous stirring by hand.
Add the sifted plain flour and rice flour to the creamed mixture. Fold gently with a spatula until the dough just comes together—try not to overmix to keep it tender.
Press this shortbread dough evenly into the prepared baking tin, using the back of a spoon or your fingers to smooth the surface. Bake for 20-25 minutes until it turns a warm golden around the edges and smells buttery.
While the shortbread bakes, prepare the caramel. In a saucepan over medium heat, melt the butter, then add the golden caster sugar and sweetened condensed milk. Stir constantly with a silicone spatula, scraping the sides, until the mixture thickens and turns a deep amber color, about 8-10 minutes. It should smell rich and caramel-y and have a glossy look.
Remove the baked shortbread from the oven and pour the hot caramel evenly over the surface. Sprinkle a pinch of flaky sea salt on top for a burst of flavor contrast. Return to the oven and bake for another 12-15 minutes until the caramel is bubbling and slightly thickened at the edges.
Allow the caramel shortbread to cool in the tin for at least 1 hour, then transfer to the fridge for two hours or until the caramel is fully set and firm to the touch.
Once cooled, lift the whole block out using the parchment paper and place on a cutting board. Warm a sharp knife in hot water, then dry it, and slice into neat squares—this helps achieve clean edges without cracking the caramel.
If you like, melt the dark chocolate and drizzle or spread it over the top for extra richness. Let the chocolate set before serving for a glossy finish.
Serve your caramel shortbread at room temperature for the perfect balance of crisp shortbread and gooey caramel, and enjoy the nostalgic crunch and rich sweetness with every bite.