From my book, Simply Sweet Nostalgic Bakes
They are a British classic, reinvented
Make the shortbread base Add the flour, butter, granulated sugar, egg yolk, vanilla extract, and salt to the bowl of a stand mixer fitted with the paddle attachment and beat until a dough forms. Press into a lined 9x9inch baking pan and bake for 25 minutes until golden
Make the caramel layer Add the condensed milk, light brown sugar, butter, golden syrup, espresso powder, salt to a heavy based sauce pan. Heat on low until the sugar has dissolved and butter melted. Then increase the heat and cook until the caramel is golden and thick. Pour over shortbread and level out
Cover in dark chocolate Add the chocolate and butter to a bowl set over a saucepan of boiling water. Make sure the water does not touch the bowl, otherwise it will seize the chocolate. Stir until the chocolate and butter have fully melted and combined. Pour over the set caramel layer and smooth with an offset spatular
Decorate dark chocolate Pipe lines of melted white chocolate over the top of the dark chocolate. With a skewer, draw the tip through the chocolate perpendicular to the lines. Go one way and then go the next creating a pretty pattern.