• Preheat the oven to 350°F and line an 8x8 square pan with parchment paper.

Shortbread

• In a large bowl, cream the butter, sugar, espresso and vanilla until creamy and smooth. The mixture doesn't need to be fluffy or pale in colour.
• Add the flour and salt and mix until just combined.
• Transfer the dough to the prepared pan and press firmly into an even layer.
• Bake for 15-20 mins until slightly golden brown on the edges, then cool. The cookie will still be soft to the touch right out of the oven, but firm up as it cools.

Caramel

• Combine all the ingredients in a medium pot or saucepan.
• Cook on medium low heat until the colour deepens into a butterscotch colour, stirring constantly. It will read around 220F on a instant read thermometer. This can take up to 30 minutes, depending on the stove.
• Pour caramel immediately onto the shortbread base, smoothing with a spatula. To get an extra smooth layer, jiggle the pan a bit.
• Refrigerate until the caramel is firm (it will not be hard).

Dark chocolate

• Once the caramel is firm, combine and melt the dark chocolate and butter in a heatproof bowl. You can either heat on medium heat in short intervals in the microwave, or melt in a double boiler.
• Pour into the pan and smooth out using a spatula, or by gently jiggling the pan.
• Melt the white chocolate and transfer to a small piping bag and pipe the designs of your choice. You could also use a spoon or toothpick, but it'll be a bit more difficult than piping.
• Let the chocolate set until hard. Slice with a sharp knife, cleaning the knife between each cut for neat slices.