Grease and line a square 20cm (8in) baking tin with nonstick baking paper. Make sure the paper hangs over the sides of the tin as we'll be using this to lift the liquorice out. Measure the remaining ingredients and have them ready as we have to work fast once the sugar mixture is done.
For the sugar mixture - Place butter, sugar, glucose, condensed milk, molasses and salt In a medium saucepan.
Place the saucepan over medium heat and stir continuously, scraping the bottom of the pan so it doesn't catch. Bring the mixture to a boil and continue to stir until the mixture reaches 120°C (248°F). If you want a softer caramel chew, remove the sugar mixture from the heat at 115°C (239°F).
Add the flour to the sugar mixture and stir quickly until smooth, then quickly stir in the anise extract. It'll make a loud sizzling sound, but this is normal.
Place a few drops of black food colouring (if using) into the sugar mixture and give it a good mix. Add more drops of colouring if needed for a darker colour. Pour the mixture into the prepared tin and tilt the tin at all angles so it spreads out evenly. Tap the tin a few times against the table to remove any large bubbles. Leave the liquorice at room temperature for an hour or until it has completely cooled and set.
For the chocolate - Place the chocolate and oil in a microwave-safe bowl and melt it in the microwave. Do this in 40-second bursts, stirring well after each burst until the chocolate has completely melted. Pour the chocolate over the liquorice, then tilt the tin on all angles for an even coating. Lightly sprinkle sea salt flakes over the chocolate, then place in the fridge for an hour until set.
Leave the tin at room temperature for 15 minutes, then cut it into little candy pieces. To prevent them from sticking together, wrap each candy in baking/parchment paper.