Step 1: Line an 8x8 inch square baking pan with parchment paper, leaving an overhang on the sides for easy removal.
Step 2: In a medium bowl, combine the crushed biscuits and 150g of melted butter. Stir until the mixture resembles wet sand.
Step 3: Press the biscuit mixture firmly into the bottom of the prepared pan. Use a flat-bottomed glass to ensure it is packed tightly. Place in the fridge to chill while you make the caramel.
Step 4: In a medium saucepan, combine the remaining 150g of butter, light brown sugar, and the sweetened condensed milk over medium-low heat.
Step 5: Stir constantly as the mixture comes to a gentle boil. Continue stirring for 5-8 minutes until the caramel thickens and turns a golden amber color.
Step 6: Pour the hot caramel over the chilled biscuit base. Spread evenly with a spatula and return to the fridge for at least 1 hour or until firm.
Step 7: In a microwave-safe bowl, melt the chocolate chips and coconut oil in 30-second intervals, stirring in between until completely smooth.
Step 8: Pour the melted chocolate over the set caramel layer and spread it to the edges. Sprinkle with a pinch of sea salt if desired.
Step 9: Refrigerate for at least 2-3 hours (or overnight) until the chocolate is firm. Lift out of the pan using the parchment paper and slice into squares with a warm knife.