Preheat your oven to 350°F (175°C). Line an 8-inch square baking pan with parchment paper, leaving some overhang on the sides to make removing the bars easier.

1. Prepare the shortbread dough.In a large bowl, cream the softened butter and sugar until smooth. Add the vanilla extract, then mix in the flour and salt until a soft, crumbly dough forms.
2. Press and bake the base.Transfer the dough to the prepared pan. Press it firmly into an even layer using the back of a spoon or your fingertips. Prick the surface lightly with a fork, then bake for 20–25 minutes, until the edges are lightly golden. Let the base cool while you prepare the caramel.
3. Make the caramel filling.In a medium saucepan, combine the condensed milk, butter, brown sugar, golden syrup, and salt. Heat over medium-low heat, stirring constantly until the butter melts and the sugar dissolves.
4. Cook until thickened.Continue stirring for about 8–12 minutes, or until the caramel thickens and turns a rich golden color. Keep the heat moderate to prevent scorching. Remove the saucepan from the heat and stir in the vanilla extract.
5. Add the caramel layer.Pour the warm caramel over the cooled shortbread base. Spread it evenly with a spatula, making sure it reaches the corners. Allow it to cool at room temperature before refrigerating for about 1 hour, or until firmly set.
6. Prepare the chocolate topping.Place the chopped chocolate in a heatproof bowl. Melt it in the microwave in 20-second intervals, stirring between each interval, or use a double boiler. If desired, stir in the coconut oil or butter for a smoother finish.
7. Spread the chocolate.Pour the melted chocolate over the chilled caramel. Gently spread it into an even layer. Let the chocolate begin to set at room temperature, then refrigerate for another 30–45 minutes until firm.
8. Slice into bars.Lift the shortbread out of the pan using the parchment paper. Let it sit at room temperature for a few minutes, then cut into squares or rectangles with a sharp knife. For clean slices, warm the knife under hot water, wipe it dry, and cut gently through each layer.