Break your chocolate into small pieces and place into your slow cooker with the condensed milk and butter. Warm the ingredients on high with the lid off for around 15 minutes until melted.
Stir the mixture with a metal or plastic spoon to ensure thoroughly melted, add the orange extract and turn your slow cooker down to low.
Stir the mixture with a metal or plastic spoon to ensure thoroughly melted and turn your slow cooker down to low.
Leave the mixture to uncovered on low for about 1hr 30 minutes, stirring every 15 minutes. Meanwhile cover a baking tin (we use a 8") with greaseproof paper & set aside.
Once your mixture has cooked for around 1hr 30 minutes, give it one last stir before transferring the mixture to your baking tray, spreading evenly and topping with your sprinkles/zest, if desired.
Leave to cool before transferring to the fridge for a couple of hours or overnight.
Cut into squares to serve.