Preheat the oven to 180C/160C Fan/Gas 5. Line an 8" square baking tin.
Make the shortbread: combine the butter and sugar with an electric mixer on high. Once totally combined, add in the flour and combine again. The mixture will look really crumbly but trust it! Press this into the lined tin, in an even layer. Bake about 20-25 mins until golden.
Remove and let cool on a wire rack. Whilst this is cooling, make the caramel.
Combine all caramel ingredients in a medium saucepan and place over medium heat. Let everything melt/combine before cranking up the heat, bringing the mixture to a boil.
Keep stirring everything for at least 5 mins whilst boiling - it will be bubbly and may splash so keep an eye on it and be careful! After about 6/7 minutes, the mixture should be golden/just edging on light brown and thickening up (keep going if not, until you reach this stage). Remove from the heat once it reaches this stage and pour it over the shortbread. Chill for at least an hour, until set.
Once the caramel has set, make the chocolate layer. Do this by breaking up the chocolate into a small bowl and microwaving in 20 second intervals, stirring in between, to prevent it from burning.
Once fully melted, pour the chocolate over the caramel layer. At this stage, add any sprinkles/decorations you want (if any) and let the whole thing set in the fridge for at least 1 hour, until the chocolate has solidified. Slice using a hot knife (hold under running hot water) and serve!