Preheat your oven to 350°F and line a 9 inch square cake tin with baking paper.
In a large bowl, mix together the flour, softened butter, and brown sugar until it forms a dough. Press the dough evenly into the bottom of the prepared cake tin.
Bake in the preheated oven for 15-20 minutes, or until golden brown. Remove from the oven and let it cool for at least 10 minutes.
In a medium-sized saucepan, combine the sweetened condensed milk, golden syrup, and extra butter. Heat the mixture over medium heat, stirring constantly until it thickens and turns a caramel color.
Pour the caramel over the cooled shortbread base, and spread it out evenly. Place the tin in the fridge for at least 30 minutes, or until the caramel is firm.
Melt the milk chocolate in the microwave or over a double boiler, and pour it over the set caramel layer. Spread the chocolate out evenly and then place the tin back in the fridge for another 30 minutes, or until the chocolate has set.
Once the chocolate is set, remove the caramel slice from the tin and slice it into squares. Enjoy!
