Preheat your oven to 160°C (320°F). Line your baking tin with parchment paper, leaving an overhang for easy removal.
In a mixing bowl, cream together the soft butter and caster sugar until the mixture becomes pale, fluffy, and fragrant—about 3 minutes. This creates a tender base for your shortbread.
Add the flour and a pinch of sea salt to the creamed butter mixture. Mix gently until just combined, forming a crumbly dough. Press this mixture evenly into the prepared baking tin, smoothing the surface with the back of a spoon.
Bake the shortbread in the preheated oven for 20-25 minutes until the edges are lightly golden. Remove from the oven and let it cool slightly on a wire rack—this helps it firm up for easier spreading of the caramel.
Meanwhile, make the caramel layer. In a saucepan over medium heat, melt the sugar until it starts to caramelize, turning a deep amber color and releasing a warm caramel aroma—about 5 minutes. Carefully add the butter, stirring until fully melted and combined.
Gradually pour in the sweetened condensed milk, stirring constantly to prevent burning. Bring the mixture to a gentle boil, then reduce heat and simmer for 5-7 minutes until thick and glossy, bubbling gently and smelling sweet and rich.
Pour the hot caramel over the slightly cooled shortbread base, spreading it evenly with a spatula. Drizzle the dark caramel or dulce de leche on top, then use a skewer or toothpick to swirl it into a marbled pattern for a beautiful, layered effect.
Allow the assembled caramel shortbread to cool at room temperature for at least 2 hours, or refrigerate for 30 minutes. This helps the caramel set and makes slicing cleaner.
Once cooled and set, use a sharp knife dipped in hot water and wiped dry to cut into neat squares. Serve at room temperature to enjoy the perfect balance of crisp, buttery crust and sticky, luscious caramel.
