Foolproof Buttery Christmas Toffee with Dark Chocolate Sea Salt

Instructions:

1. Line an 8x8 inch (20cm x 20cm) pan with parchment paper or a silicone mat, ensuring there is an overhang on two sides to use as handles later. Lightly grease the liner.
2. In a heavy-bottomed saucepan (at least 3-quart capacity), combine the butter, sugar, water, corn syrup, and fine sea salt.
3. Place over medium heat and stir constantly until the butter is melted and the sugar is completely dissolved. Do not let it boil yet. Wipe down the sides of the pan with a damp pastry brush to remove any stray sugar crystals.
4. Stop stirring once the mixture begins to boil vigorously. Insert the candy thermometer and allow the mixture to cook undisturbed until the temperature reaches exactly 300°F (149°C) to 310°F (154°C) (Hard Crack stage).
5. Immediately remove the pan from the heat. Let the bubbling subside for about 30 seconds. Do not stir the mixture at this point.
6. Carefully pour the hot toffee mixture into the prepared pan. Gently tilt the pan to encourage the toffee to spread evenly to the edges. Do not scrape the pan.
7. Allow the toffee to cool completely and harden at room temperature for a minimum of 1 hour.
8. Gently melt the dark chocolate using a double boiler or in short bursts in the microwave, stirring every 30 seconds until smooth.
9. Pour the melted chocolate evenly over the hardened toffee slab. Immediately sprinkle the flaky sea salt generously over the chocolate before it sets.
10. Allow the chocolate topping to set completely (about 30 minutes). Use the parchment overhang handles to lift the entire slab from the pan, and break the toffee into irregular, satisfying shards for serving.