Preheat oven to 350°F (175°C). Line an 8x8 inch square baking pan with parchment paper.

Make the Shortbread: In a large bowl, combine flour and sugar. Cut in cold butter until the mixture resembles coarse crumbs.

Press the mixture firmly into the prepared pan. Bake for 20-25 minutes, or until lightly golden brown. Let cool completely.

Make the Caramel: In a medium saucepan, combine butter, sweetened condensed milk, golden syrup, and salt. Cook over medium heat, stirring constantly, until the butter is melted and the mixture comes to a gentle boil.

Reduce heat to low and continue to cook, stirring constantly, for 10-15 minutes, or until the caramel is thick and golden brown.

Pour caramel over cooled shortbread. Let set for at least 30 minutes, or until firm.

Melt the chocolate in a double boiler or microwave. Spread over the caramel layer.

Sprinkle with sea salt (optional). Chill in the refrigerator for at least 1 hour, or until the chocolate is firm.

Lift out of the pan using the parchment paper. Cut into squares and serve.