Heat the oven to 180°C. Cream the butter and sugar until pale and fluffy. Add the flour, baking powder and salt and combine. Spread the dough in a square tin lined with parchment paper. To get a flat surface, cut a parchment paper into a square shape and flatten it with your hands.
Bake for 25 minutes, let cool in the tin for 15 minutes then remove from tin and let cool completely. Cut into 2 rectangles to fit the size of a loaf tin.
Make the caramel: place all the ingredients in a small saucepan and melt over medium to low heat. Turn the heat slightly up and bring to a boil, stirring constantly so it doesn’t burn for at least 10 minutes. When it gets to a toffee colour, remove from the heat and let cool.
Place a sheet of thick paper inside a loaf tin to create a round shape. Cover with parchment paper and pour some chocolate to create a thin layer on all sides. Refrigerate.
To assemble the bar, pour the caramel into the loaf tin, then place the two rectangular biscuits, pressing down slightly. Pour a thin layer of melted chocolate and let cool slightly. Fold the parchment paper and place in the freezer for one hour.
After an hour, remove the bar from the tin and place on two ramekins over a tray, the side with the chocolate down. Pour some melted chocolate and let cool completely before serving.