Step 1: Prepare the Biscuit Base. In a food processor, crush the ginger biscuits into fine crumbs. Alternatively, place them in a zip-lock bag and crush with a rolling pin.
Step 2: Combine crumbs with melted butter. In a mixing bowl, combine the biscuit crumbs with the melted butter. Mix until the crumbs are evenly coated.
Step 3: Press into pan. Line an 8×8 inch square baking pan with parchment paper. Press the biscuit mixture firmly into the bottom of the pan to create an even base. Use the back of a spoon to pack it down tightly.
Step 4: Chill the base. Place the pan in the refrigerator to set while you prepare the caramel filling.
Step 5: Make the Caramel Filling. In a saucepan over medium heat, combine the sweetened condensed milk, brown sugar, butter, golden syrup, and ground ginger.
Step 6: Cook the caramel. Stir continuously until the mixture comes to a gentle boil. Reduce the heat and continue to cook for about 5-7 minutes, stirring constantly, until it thickens and turns a rich golden caramel color. For more details on caramelizing, refer to Serious Eats’ Guide to Caramel.
Step 7: Pour the Caramel. Carefully pour the hot caramel filling over the chilled biscuit base, spreading it evenly.
Step 8: Set the caramel. Return the pan to the refrigerator to set for about 30 minutes.
Step 9: Prepare the Chocolate Topping. In a microwave-safe bowl or using a double boiler, melt the dark chocolate with the coconut oil (if using) until smooth and glossy.
Step 10: Pour over caramel. Once the caramel layer has slightly set, pour the melted chocolate over the caramel, spreading it evenly.
Step 11: Final Chill. Return the slice to the refrigerator and chill for at least 2 hours, or until the chocolate is fully set.
Step 12: Cut and Serve. Once set, lift the slice out of the pan using the parchment paper. Cut into squares or bars using a sharp knife. Serve chilled and enjoy!