Melt together butter and golden syrup in a small saucepan. Once melted add the bicarbonate and boiling water.
Mix into the dry ingredients.
Press into a lined tin and cook for 15 minutes or until lightly brown. Removed from oven and let it cool.
Caramel
Melt butter in saucepan and add condensed milk and golden syrup and stir continuously on low heat until it is thick (usually around 10 minutes). Make sure you scape the bottom regularly so nothing burns.
Pour caramel over the top of the base and put back in the oven for around 10 minutes, until the edges of the caramel are golden.
Then pour 180g melted dark chocolate over the top of the caramel and sprinkle some salt on top if you like.
Refrigerate for 3 hours or until set and cold. Slice and serve.