Pre-heat oven to 175℃/350℉. Line your baking tray with parchment paper, making sure there is ample overhang to easily remove slice when complete.
To make the shortbread - In a large bowl, beat your butter, sugar, vanilla bean paste and egg yolk for about 90 seconds. Add flour, mix until the flour just disappears. Do not over-mix.
Add the shortbread mix to the base of the baking tray and press it down firmly with your hands, or the bottom of a glass, until it is evenly spread all over the base and in the corners. Bake for approximately 20 minutes, until you see it turn slightly golden in colour in parts. Remove from oven and allow to cool.
To make the caramel, add all the caramel ingredients into a saucepan (or as I prefer- a non stick frypan - it's easier to get into those corners with your whisk), melt over med-high heat, mixing continuously. You'll see/feel the caramel start to pull away from the edges, this is when you temp it with your digital thermometer. Keep mixing until it reaches 106℃/223℉, then remove from the heat. Pour over the shortbread base and spread it evenly. Chill in the fridge for about 20 minutes before making the chocolate layer.
For the chocolate, add chocolate and cream into a microwave safe bowl. Heat for 30 seconds on high, mix well. Heat for 20 seconds on high. Mix. This should be sufficient heat to melt all the chocolate, just keep mixing. Spread the chocolate evenly over the caramel and leave to set in the fridge.
Cut into squares when your caramel slice is completely chilled. In hotter climates, keep in refrigerator, or in colder climates keep at room temperature.